B  E  R  K  E  LEY\ 

JBRARY 

F 


LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 

Class 


THE 


EARTH  AND  ITS  STORY 


A  FIRST  BOOK  OF 


BY 


ANGELO  HEILPEIN 

v^ 

PROFESSOR  OF  GEOLOGY  IN  THE  ACADEMY  OF  NATURAL  SCIENCES 
OF  PHILADELPHIA 


SILVER,  BURDETT  AND  COMPANY 
NEW  YORK  .  .  BOSTON  .         .  CHICAGO 


LIBRARY 


COPYRIGHT,  1896, 
BY  ANGELO  HEILPRIN. 


OF   THE 

UNIVERSITY 

OF 


PREFACE. 


IN  the  preparation  of  this  volume  it  has  been  the 
aim  of  the  author  to  present  briefly,  forcibly,  and  possi- 
bly in  a  more  popular  form  than  in  most  books  of  a 
similar  nature,  the  general  facts  of  geology.  In  its 
relation  to  the  more  advanced  and  technical  treatises 
on  the  subject  this  work  may  stand  as  introductory, 
and  yet  independent  by  itself.  While  its  treatment  of 
the  science  of  geology  is  not  burdened  with  numberless 
details,  nor  made  too  analytical  in  method,  it  is  be- 
lieved to  be  sufficiently  comprehensive  to  meet  the 
needs  of  the  average  student,  and  to  appeal  to  the 
large  class  of  readers  who  would  pass  by  a  difficult 
technical  work,  and  at  the  same  time  would  not  be 
satisfied  with  a  mere  elementary  text-book. 

The  author  is  conscious  of  the  difficulty  of  compress- 
ing into  a  limited  space  the  mass  of  material  that 
bears  upon  the  subject,  and  has  found  it  necessary  to 
leave  untouched  many  points  which  might  otherwise 
have  been  exhibited.  It  is  thought,  however,  that 
nothing  has  been  omitted  which  is  vitally  essential  to  a 
complete,  popular  treatise ;  and  perhaps  the  combination 
of  brevity,  compactness,  and  fulness  in  the  work,  while 
not  over-taxing  the  patience  of  the  reader,  will  secure 
from  him  a  larger  amount  of  attentive  study  than  if 

196434 


4  PREFACE. 

the  volume  were  more  extended  and  technical  in  its 
character. 

The  illustrations  are,  in  the  main,  reproductions  from 
photographs  taken  in  the  field,  and  are,  therefore,  trust- 
worthy in  their  representations.  A  mere  sketch  or  dia- 
gram, which  has  hitherto  been  the  principal  resource  of 
geological  text-books,  has  none  of  the  advantages  of  a 
perfect  photographic  picture  of  Nature,  and  while  cer- 
tainly useful  in  its  place,  fails,  as  most  teachers  well 
know,  to  harmonize  the  facts  of  the  classroom  with 
those  of  the  field. 

The  work  is  commended  to  classes  in  high  schools 
and  colleges,  and  also  to  the  large  and  increasing  num- 
ber of  lay  readers  who  are  desirous  of  knowing  more 
about  the  formation,  structure,  and  development  of  the 
earth  on  which  they  live.  As  students  they  will  find 
new  wonders  in  the  structural  history  and  the  rare  phe- 
nomena which  science  is  continually  unfolding  from 
earth  and  sea. 

It  is  but  proper  to  add  acknowledgment  to  the  many 
friends  who  have  so  kindly  assisted  the  author,  espe- 
cially in  the  securing  and  preparation  of  photographic 

material. 

A.  H. 

ACADEMY  OF  NATURAL  SCIENCES, 

PHILADELPHIA,  June,  1896. 


CONTENTS. 


CHAPTER  I. 
WHAT  THE  KOCKS  TEACH. 

THE  Decay  of  Rocks.  —  The  Causes  of  Decay  in  Rocks.  —  The  Weather- 
ing of  Rocks.  —  Desert  Sands  and  Deserts.  — The  Course  of  Mud 
and  Sand pp.  13-19 

CHAPTER  II. 
SOME  OF  OUR  COMMONER  ROCKS,  AND  HOW  THEY  ARE  MADE. 

Sandstone.  —  Pebble-Rocks  or  Conglomerates  (Pudding-Stones).  —  Where 
the  Materials  of  Sandstone  come  from.  —  Limestones  and  Marbles. 
—  Organic  Nature  of  Limestones. — The  Obliteration  of  Organic 
Traces.  —  Coquina  Rock.  —  Chalk.  —  Oceanic  Ooze ;  Globigerina 
Ooze. —  Flags,  Shales,  and  Slates. —  Granite.  — Distinct  Types  of 
Granite.  —  Origin  of  Granite. —Igneous  and  Aqueous  Rocks.— 
Gneiss.  —  Origin  of  Gneiss.  —  Mica  Schists  and  other  Schists. 

pp.  20-35. 
CHAPTER  III. 

WHAT  ROCKS  LOOK  LIKE  IN  THE  FIELD. 

Fossil  Imprints ;  Ripples.  —  Footprints ;  Raindrops.  —  What  Rock- 
Strata  Signify.  —  Disturbed  Rock-Masses.  —  Rock-Folding.  —  The 
Positions  occupied  by  Rocks ;  Dip pp.  36-43 

CHAPTER  IV. 
WHAT  A  MOUNTAIN  TEACHES. 

How  Mountains  may  be  formed.  —  Mountains  of  Simple  Folding; 
Strike,  Anticlines,  Synclines.  —  Overturnings  and  Mountain  Travel 
(Shearing). — Fallen  Blocks  of  the  Crust;  Continental  Buttresses 
(Horsts).  —  Crustal  Breakages  and  Mountain-Making.  —  How  Water 
Works.  —  Earth  Pillars  and  Monuments.  —  Ravines,  Gorges, 
Gulches.  —  The  Base-Level  of  Erosion ;  Peneplain.  —  Canons.  — 
Old  and  New  Features  in  a  Landscape ;  Valleys.  —  Mountain  Val- 
leys and  the  Conditions  of  Scenery.  —  Transverse  Valleys;  Water 

5 


6  CONTENTS. 

Gaps.  —  The  Origin  of  Gaps.  —  River  Terraces.  —  The  Silting 
of  Rivers.  —  Meadow-Lands.  —  Origin  of  Lake  Basins ;  Crater 
Lakes ;  Glacial  Lakes.  —  Ancient  Lake  Basins ;  Lake  Terraces.  — 
The  Scenery  of  Lake-Shores pp.  44-64 

CHAPTER  V. 
SNOW  AND  GLACIERS. 

Snow-Line.  — The  Mountain  Snows  and  What  becomes  of  Them.  —  What 
a  Glacier  is.  —  The  Moraine ;  Glacial  Striae ;  Erratics.  —  Terminal 
and  Lateral  Moraines. — The  Forming  Basin  of  the  Ice  (Neve  or 
Firn).  — Compound  Glaciers;  Medial  Moraines  ....  pp.  65-74 

CHAPTER  VI.  . 
THE  WORK  OF  GLACIERS. 

The  Flow  of  Glaciers.  —  The  Rate  of  Glacial  Movement.  —  Glacial  Scour 
and  Polish ;  Roches  Moutonnees.  —  Drift.  —  The  Retreat  of  Glaciers. 

—  Distribution  and  Dimensions  of  Glaciers. —Evidences  of  Past 
Glaciation;    Great    Ice   Age.  —  The    Great    Terminal    Moraine.— 
Cause  of  the  Great  Ice  Age pp.  75-86 

CHAPTER  VII. 

THE  WORK  OF  UNDERGROUND  WATERS. 

Mineral  Waters.  —  The  Formation  of  Caves.  —  Cave-rifts  and  Bone- 
Caves.  —  Natural  Bridges.  —  Stalactites  and  Stalagmites ;  Ice-Caves. 

—  Hot  Springs  and  Geysers pp.  87-93 

CHAPTER  VIII. 

THE  RELATIONS  OF  THE  SEA  TO  THE  LAND,  OR  WHAT  THE  SEA 

DOES  AND  WHAT  IT  UNDOES. 

Configuration  of  the  Oceanic  Trough.  —  The  Origin  of  the  Oceanic 
Trough.  —  Permanency  or  Non-Permanency  of  Continents  and 
Oceans.  —  Disruption  of  Continental  Masses.  —  Configuration  of  the 
Atlantic  Basin. —  Inconstancy  of  the  Ocean-Level;  Oceanic  Trans- 
gressions and  Recessions.  —  Drowned  Lands  and  Waters.  —  Fjords ; 
Strands  and  Ocean  Terraces.  —  Wear  of  the  Shore-Line ;  Plain  of 
Marine  Denudation.  —  The  Dismemberment  of  the  Land  by  the 
Sea.  —  The  Ocean  as  a  Receiving  Basin.  —  The  Sediment  Discharge 
of  Rivers.  — The  Making  of  New  Land  .  ..."...  pp.  94-110 

CHAPTER  IX. 
THE  EARTH  IN  ITS  INTERIOR. 

The  Internal  Heat.  —  Pockets  of  Molten  Material.  —  The  Density  or 
Weight  of  the  Earth pp.  111-116 


CONTENTS.  1 

CHAPTER  X. 
VOLCANOES  AND  WHAT  THEY  TEACH. 

The  Aspects  of  a  Volcano ;  Vesuvius.  —  The  Operations  of  a  Volcano. 

—  The  Characteristics  of  a  Volcano.  —  Dimensions  of  Volcanoes.  — 
Composite  Cinder  and  Ash  Cones.  —  Lava  (Basalt),  Scoriae,  and  Ash. 

—  The  Working  Activity  of  Volcanoes.  —  Shifting  of   the   Points 
of  Activity;   Parasitic   Cones.  —  The  After-History  of  a  Volcano. 

—  The  Causes  of  Eruption.  —  Fissure  Eruptions.  —  Laccolites. 

pp.  117-129 

CHAPTER  XI. 
DISTRIBUTION  OF  VOLCANOES  AND  EARTHQUAKES. 

Distribution  of  Active  Volcanoes.  —  Earthquakes.  —  Passage  of  the 
Earthquake  Waves. — Intensity  of  Movement.  —  "Tidal  "or  Oceanic 
Waves pp.  130-137 

CHAPTER  XII. 
CORALS  AND  CORAL  ISLANDS 

The  Aspects  of  a  Coral  Reef. —  The  Making  of  Coral  Land. —The 
Kinds  of  Coral  Islands.  —  Occurrence  in  Deep  Water ;  Formation  of 
Reefs.  — Thickness  of  Coral-made  Rock.  —  Subsidences.  —  The 
Atoll  Lagoon.  —  Elevated  Reefs.  —  Distribution  of  Modern  Reefs. — 
Ancient  Reefs pp.  138-149 

CHAPTER  XIII. 
FOSSILS  AND  THEIR  TEACHINGS. 

What  a  Fossil  is.  —  Manner  of  Occurrence  of  Fossils.  —  Progression 
in  Structure.  —  The  Time-Standard  of  Geological  History. —  The 
Variation  and  Extinction  of  Animal  Forms.  —  Geological  Epochs 
and  Formations.  —  Faunal  Characteristics.  —  Kinds  of  Fossils ; 
Marine,  Terrestrial,  and  Fresh-Water.  —  The  Origin  of  the  Differ- 
ent Kinds  of  Faunas.  —  The  Succession  of  Life.  —  Faunas  of  the 
Early  Periods  (Paleozoic).  —  Faunas  of  the  Middle  Periods  (Meso- 
zoic).  —  Faunas  of  the  Newer  Periods  (Cainozoic)  .  .  .  150-164 

CHAPTER  XIV. 

THE  ORGANIZATION  OF  SOME  OF  THE  LESS-KNOWN  GROUPS  OF 
FOSSILS. 

Foraminifera.  —  Trilobites.  —  Crinoids  or  Stone-Lilies.  —  Brachiopods. 

—  Ammonites  and  their  Allies.  —  Belemnites   ....     pp.  165-174 


8  CONTENTS 

CHAPTER  XV. 
FOSSIL  FISHES,  BIRDS,  REPTILES,  AND  QUADRUPEDS. 

Fossil  Fishes.  —  Reptiles.  —  Pterodactyls.  —  Archseopteryx.  —  Birds.  — 
Mammalia  (Quadrupeds).  —  Origin  of  Existing  Faunas.  —  Ances- 
tral Forms  of  Animals.  —  The  Age  of  Man  and  the  Mammoth. 

pp.  175-184 

CHAPTER   XVI. 
THE  PHYSIOGNOMY  OF  THE  LAND-SURFACE. 

Physiognomy  of  Continents.  —  Physiognomy  of  Mountains.  —  The  Phys- 
iognomy of  Plateaus  and  Plateau  Mountains.  —  The  Physiognomy  of 
Valleys.  —  Physiognomy  of  the  Coast-Line.  —  The  Physiognomy  of 
Rock-Masses.  — Unconformity  in  Succession.  —  Characters  impressed 
upon  Rock-Masses  .  . , pp.  185-206 

CHAPTER  XVII. 

SOME  OF  THE  COMMON  AND  MORE  USEFUL  METALS  AND  MINERALS. 

Gold.  —  Silver.  —  Copper.  —  Zinc.  — Tin.  —  Lead.  — Antimony.  —  Arse- 
nic. —  Nickel.  —  Iron.  —  Manganese.  —  Mercury.  —  Platinum.  — 
Aluminium.  —  Sulphur.  —  Graphite  (Plumbago).  —  Rock  Salt.  — 
Gypsum.  —  Coal.  —  Petroleum ;  Natural  Gas.  —  Asphaltum. 

pp.  207-231 
CHAPTER  XVIII. 

BUILDING-STONES,  SOILS,  AND  FERTILIZERS. 

Building-Stones.  —  Flagging-Stones.  —  Roofing-Slates  and  Tile-Stones. 
—  Clays  and  Soils.  —  Fertilizers ;  Lime,  Guano,  Phosphates. 

pp.  232-241 

CHAPTER  XIX. 

SOME  OF  THE  COMMONER  ROCK-FORMING  MINERALS  AND  MINERALS 
OCCURRING  IN  ROCKS. 

Quartz.  —  Amethyst.  —  Opal.  —  Calcite.  —  Feldspar.  —  Mica.  —  Horn- 
blende. —  Asbestus.  —  Pyroxene.  —  Garnet.  —  Tourmaline.  —  Flu- 
orite.  —  Apatite.  —  Beryl.  —  Emerald.  —  Topaz.  —  Cryolite.  — 
Turquoise. — Ruby. — Diamond pp.  242-253 


TEACHERS'  REFERENCES pp.  254-262 

INDEX pp.  263-267 


LIST  OF  ILLUSTRATIONS. 


Plate  1.  — ROCK  DISINTEGRATION Opposite  page  14 

1.  Granite  bowlders,  Rocky  Mountains. 

2.  Trap-rock  of  Pottstown,  Pa.  —  a  "  Felsenmeer." 

Plate  2.  — ROCK  DISINTEGRATION "  15 

1.  Mountain  disintegration  in  the  Alps. 

2.  ^Eolian  rock  of  the  Bermudas. 

Plate  3.  — STRUCTURE  OF  ROCKS  , "  20 

1.  A  piece  of  granite. 

2.  A  piece  of  gneiss. 

Plate  4. —  STRUCTURE  OF  ROCKS •*  21 

1.  A  piece  of  pudding-stone. 

2.  A  piece  of  shell-rock,  coquina. 

3.  Fragment  of  crinoidal  limestone. 

Plate  5. —ROCK  IMPRESSIONS "  38 

1.  Ancient  ripples. 

2.  Triassic  shale,  with  sun-cracks  and  footprints. 

Plate  6.  — ROCK  IMPRESSIONS "  39 

Triassic  shale,  showing  track  of  a  reptile. 
Plate  7. —THE  POSITIONS  OF  ROCK-MASSES      ....  "  42 

1.  Horizontal  strata,  near  Quebec. 

2.  Outcrop  of  coal  in  the  Pennsylvania  region. 

Plate  8. —  THE  POSITIONS  OF  ROCK-MASSES      ....  "  43 

1.  Limestone  strata  near  Philadelphia. 

2.  Limestone  along  the  Schuylkill  River. 

Plate  9.  —  THE  POSITIONS  OF  ROCK-MASSES      ....  "  46 

1.  Anticlinal  arch  near  Hancock,  Md. 

2.  A  synclinal  fold  in  coal. 

Plate  10. —THE  POSITIONS  OF  ROCK-MASSES   ....  "  47 

1.  Folded  strata  of  sandstone. 

2.  Folded  beds  of  limestone. 

Plate  11.  — THE  POSITIONS  OF  ROCK-MASSES    ....  "  50 

1.  Gneiss  of  the  Wissahickon  Valley,  Pa. 

2.  Creep. 

Plate  12.  — THE  POSITIONS  OF  ROCK-MASSES    ....  "  51 

1.  Limestone  of  the  Schuylkill  Valley,  Pa. 

2,  Folded  gneiss  of  Philadelphia. 

Plate  13.  — THE  CANTON  OF  THE  ARKANSAS.  — "  ROYAL  GORGE,"    "  54 

9 


10  LIST  OF  ILLUSTRATIONS. 

Plate  14. —  RIVER  EROSION Opposite  page  55 

The  Grand  Cafion  of  the  Colorado. 

Plate  15. -»-THE  WORK  OF  RIVERS "  56 

1.  River-cut  at  Glenwood  Springs,  Col. 

2.  Gap  of  the  Bow  River,  Alberta. 

Plate  16.  — THE  WORK  OF  RIVERS "  57 

1.  The  Delaware  above  the  Water  Gap,  Pa. 

2.  The  Grand  River,  region  of  the  Yellowstone. 

Plate  17.  —  DENUDATION  OF  THE  LAND-SURFACE   ...  4<  58 

1.  A  V-shaped  valley  in  the  Alps. 

2.  The  Vale  of  Cashmere. 

Plate  18.  — DENUDATION  OF  THE  LAND-SURFACE    ...  "  59 

A  ^-shaped  valley  in  the  Utah  Desert. 

Plate  19. —  DENUDATION  OF  THE  LAND-SURFACE   ,  "  60 

The  Giant's  Club,  near  the  Green  River,  Wyoming 

Plate  20.  — RECONSTRUCTION  OF  THE  LAND-SURFACE    .       .  "  61 

1.  Lake  Bonneville. 

2.  The  valley  of  Engelberg,  Switzerland. 

Plate  21.  — OCEANIC  DESTRUCTION       ......  "          104 

1.  Marine  arches,  Ireland. 

2.  The  island  of  Torghatten,  Norway, 

Plate  22.  — THE  WORK  OF  UNDERGROUND  WATERS       .  "  88 

The  Hermannshohle,  Harz  Mountains. 

Plate  23.  — THE  WORK  OF  UNDERGROUND  WATERS       .  "  89 

1.  The  bone-cave  of  Gailenreuth,  Bavaria. 

2.  Plan  of  Mammoth  Cave. 

Plate  24.  — THE  PHYSIOGNOMY  OF  A  GLACIAL  REGION.       .  "  66 

The  Donkin  Glacier,  Alberta,  Canada. 

Plate  25.  — THE  ASPECT  OF  A  GLACIER "  67 

The  Rhone  Glacier,  Switzerland. 

Plate  26.  — THE  ASPECT  OF  A  GLACIER "  68 

Hallett  Glacier,  Col. 

Plate  27.  — THE  ASPECT  OF  A  GLACIER "  69 

The  Mer-de-Glace,  Switzerland. 

Plate  28.  — GLACIAL  PHENOMENA "  70 

1.  A  striated  rock-slab. 

2.  The  front  wall  of  a  Greenland  glacier. 

Plate  29.  — THE  PHYSIOGNOMY  OF  GLACIERS    ....  74 

1.  The  Aletsch  Glacier,  Switzerland. 

2.  The  Fan  Glacier,  North  Greenland. 

Plate  30. —  THE  ASPECT  OF  A  GLACIATED  REGION         .       .  75 

1.  The  summit  of  the  Shawangunk  Mountains. 

2.  A  glaciated  rock  near  Halifax,  N.S. 

Plate  31.— THE  WORK  OF  GLACIERS 80 

1.  Rock-surface  planed  by  glacial  passage. 

2.  The  roches-nioutonnees  of  the  Grimsel,  Switzerland. 


LIST  OF  ILLUSTRATIONS.  11 

Plate  32.  — THE  WORK  OF  GLACIERS Opposite  page  81 

1.  The  great  moraine  of  Pennsylvania. 

2.  Section  of  a  moraine. 

Plate  33.— THE  WORK  OF  HEATED  WATERS    ....  "  91 

1.  Giant  Geyser,  Yellowstone  National  Park. 

2.  A  hot-spring  in  the  Yellowstone  region. 

Plate  34.  — THE  WORK  OF  HEATED  WATERS    ....  "  92 

1.  Crow's  Nest  Geyser,  New  Zealand. 

2.  Castle  Geyser,  Yellowstone  National  Park. 

Plate  35.  — THE  WORK  OF  HEATED  WATERS  ....  "  93 

The  White  Terrace  of  liotomahana,  New  Zealand. 

Plate  36.  — VOLCANIC  PHENOMENA "  117 

Fusiyama,  Japan. 

Plate  37.  — VOLCANIC  PHENOMENA "          118 

1.  The  cone  of  Vesuvius. 

2.  The  Vesuvian  crater. 

Plate  38.  — VOLCANIC  PHENOMENA "  119 

1.  Lava-flow  from  Kilauea,  Sandwich  Islands. 

2.  Lava-flow  from  Mauna  Loa. 

Plate  39.  — VOLCANIC  PHENOMENA "  120 

Crater  of  Kilauea,  Sandwich  Islands. 
Plate  40.  — VOLCANIC  PHENOMENA "  121 

Volcano  of  Tarawera,  New  Zealand. 
Plate  41.  —  VOLCANIC  PHENOMENA "          122 

Whatipoho,  New  Zealand. 
Plate  42.  — VOLCANIC  PHENOMENA "          124 

1.  The  trap-dike  of  West  Conshohockeu,  Pa. 

2.  The  Giant's  Causeway,  Ireland. 

Plate  43.  — VOLCANIC  PHENOMENA      ......  "          125 

Orange  Mountain,  N.J. 
Plate  44.  — VOLCANIC  PHENOMENA "          126 

"  Mato  Tepee,"  Wyoming. 
Plate  45.  —  CORALS  AND  CORAL  ISLANDS "  138 

1.  The  seolian  rock  of  the  Bermudas. 

2.  The  Great  Barrier  Keef  of  Australia. 

Plate  46.  —  CORALS  AND  CORAL  ISLANDS "          139 

1.  A  fan-coral. 

2.  A  brain-coral. 

Plate  47.  —  CORALS  AND  CORAL  ISLANDS "          140 

1.  Rose  coral  (Isophyllia). 

2.  Branch  of  Oculiiia. 

3.  Millepore. 

Plate  48. —  THE  PHYSIOGNOMY  OF  MOUNTAINS  .       ...  188 

1.  The  Aiguille  du  Dru,  Savoy,  France. 

2.  The  Bee-Hive  Mountain,  Alberta,  Canada. 

Plate  49.—  THE  PHYSIOGNOMY  OF  MOUNTAINS         ...  189 

1.  The  Wetterhorn,  Switzerland. 

2.  The  Book  Cliffs,  Utah, 


12  LIST  OF  ILLUSTRATIONS. 

Plate  50.  — THE  PHYSICS  OF  MOUNTAIN-MAKING     .       .        Opposite  page  202 
Plate  51.  — ROCK  FOLDS  AND  DISTURBANCES    ....  "          203 

Plate  52.  —  FOSSILS "          150 

Block  of  rock  crowded  with  Ammonites. 

Plate  53. -FOSSILS "          168 

1,  3.   Crinoids,  or  "  stone  lilies." 

4.  Trilobite. 

5.  Glyptocrinus. 

Plate  54.  —  FOSSILS.  —  TBILOBITES '  169 

1.  Homalonotus. 

2.  Head  of  Phacops. 

3.  Phacops. 

4.  Homalonotus. 

5.  Paradoxides. 

Plate  55.  — FOSSILS. —TYPES  OF  BRACHIOPODS        ...  170 

Plate  56.  —  FOSSILS.  —  TYPES  OF  CEPHALOPODS        ...  "          171 

Plate  57.  — FOSSILS 176 

1.  Archseopteryx. 

2.  Pterodactyl. 

Plate  58.  — FOSSILS "          177 

1.  Plesiosaurus. 

2.  Ichthyosaurus. 

3.  Clidastes. 

4.  Ichthyornis. 

5.  Hesperornis. 

Plate  59.  —  FOSSIL  REPTILES "          180 

1.  Stegosaurus. 

2.  Brontosaurus. 

3.  Triceratops. 

Plate  60.  —  ANCESTRAL  FORMS  OF  THE  HORSE  .       ...  "          181 

Plate  61.  — RESTORATIONS  OF  TERTIARY  QUADRUPEDS  .       .  182 

1.  Mastodon. 

2.  Uintatherium. 

3.  Helladotherium. 

4.  Oreodon. 

Plate  62.  —  FOSSILS  OF  THE  POST-PLIOCENE  PERIOD      .  "          183 

1.  Glyptodon. 

2.  Megatherium. 

3.  Mylodon. 

4.  Skull  of  a  sabre-toothed  cat. 

Plate  63.  —  SOME  FORMS  OF  CRYSTALS       .  "          242 

1.  Quartz  (hexagonal  prism).     2.    Zircon.     3.   Fluorite  (oc- 
tahedron).   4.  Garnet  (trapezohedron). 

5.  Quartz  (modified  hexagonal  prism).     6.  Rock-Salt  (cube). 
7.  Gypsum.    8.  Quartz.     9.  Calcite  (rhombohedron). 

10.  Emerald  (hexagonal  prism).     11.  Gypsum.    12.  Topaz. 

13.  Staurolite  (intercrossing-twin). 
Plate  64.  —  GLACIATED  REGION    OF   THE    NORTH-EASTERN 

UNITED  STATES  AND  SOUTHERN  CANADA    .  Opposite  page  86 


THE  EARTH  AND  ITS  STORY 


PART    I. 


CHAPTER   I. 

WHAT    THE    BOCKS    TEACH. 

MOST  persons  have  rather  vague  notions  regarding 
rocks.  In  my  daily  walks  through  a  neighbor's  field 
I  pass  a  great  rock,  which  has  stood  there  for  hundreds 
of  years  before  I  was  born,  and  my  farmer  friend  tells 
me  that  it  grew  there,  and  that  it  still  grows.  As  with 
many  other  things  that  take  place  on  the  earth,  and  of 
which  we  know  little,  we  believe  what  we  are  told,  and 
ask  few  questions.  Our  worthy  farmer  had  not  seen 
this  one  rock  actually  growing;  but  he  had  observed 
that  other  rocks  or  stones  which  were  new  to  him 
appeared  upon  his  field,  and  he  concluded  that  they 
came  there  by  growing.  He  did  not  ask  himself  how 
they  grew,  or  how  anything  could  grow  without  having 
real  life  in  it ;  but  he  was  satisfied,  just  as  hundreds  of 
thousands  of  other  people  are,  with  the  simple  fact  as  it 
appeared  to  him. " 

The  Decay  of  Rocks.  —  In  truth,  however,  that  rock, 
like  almost  every  other  rock,  grows  only  in  one,  way  - 

13 


14  THE  EARTH  AND  ITS   STORY. 

smaller  and  smaller  every  year,  every  month  of  that 
year,  and  every  day  of  the  month.  We  all  know  how 
readily  rock  crumbles.  We  can  hardly  go  anywhere 
in  the  country  without  meeting  with  some  proof  of  it. 
The  very  dust  that  lies  in  the  roadway  is  a  part  of 
the  underlying  rock  or  stone,  powdered  in  one  way  or 
another;  the  mud  through  which  you  have  struggled 
so  hard  to  make  your  way  is  the  same  material  mixed 
with  water;  and  the  bowlders  that  lie  at  the  foot  of 
the  mountain  side  are  merely  parts  of  the  mountain 
that  have  broken  away  and  fallen  to  the  bottom.  Even 
about  the  big  rock  which  has  so  long  troubled  farmer 
Smithers,  I  to-day  found  bits  and  fragments  of  its  own 
materia-1  scattered,  so  that  here,  as  elsewhere,  the  evi- 
dence of  destruction  is  plainly  visible.  We  have 
learned  our  first  lesson  in  geology:  All  rocks  undergo 
destruction  or  decay,  and  sooner  or  later  disappear. 

The  Causes  of  Decay  in  Rocks.  —  When  we  ask  our- 
selves the  question  why  it  is  and  how  it  is  that  rocks 
crumble  or  decay,  it  is  not  easy  to  give  the  same  answer 
for  all  cases.  Some  rocks  crumble  in  one  way,  and 
some  in  another;  some  rocks  are  much  tougher  than 
others,  and  stand  apparently  unchanged  for  perhaps  a 
century,  while  others  decay  so  rapidly  that  they  are  chan- 
ging with  almost  every  day.  One  of  the  surest  ways  to 
destroy  a  rock  is  to  allow  water  to  soak  into  its  joints 
or  pores,  and  there  do  just  what  it  often  does  in 
winter  in  the  water-pipes  of  your  own  house  :  it  freezes, 
and,  by  expanding,  forces  the  mass  apart.  Tons  of  rock 
are  in  this  way  split  off  from  the  mountain  side  every 
winter;  but  although  the  force  is  great,  that  does  not 
prevent  i£  from  splitting  off  small  fragments.  Large 


EOCK  DISINTEGRATION. 

1.  Granite  breaking  into  bowlders,  Rocky  Mountains. 

2.  Disintegrated  trap-rock  of  Pottstown,  Pa.,—  a  "  Felsenraeer." 


I 


HOCK  DISIXTJ 


1.  Mountain  disintegration  in  the  Alps;  the  accumulated  debris  on  the  right  consti- 

tutes  a  "Talus." 
8,   Weathered  aiolian  rock  of  the  Bermudas. 


WHAT  THE  EOCKS  TEACH.          15 

and  small,  they  all  go  to  the  destruction  of  the  rock. 
So  well  does  the  stone-cutter  know  this  method  of 
breaking  rock,  that  oftentimes,  in  quarrying  for  his 
blocks,  he  simply  inserts  a  number  of  wooden  stakes  in 
drill-holes,  allows  these  to  expand  by  water,  and  then 
waits  for  the  inevitable  result. 

Another  way  in  which  rock  crumbles  is  through  .the 
alternate  swelling  and  contraction  which  it  undergoes 
in  passing  through  extremes  of  temperature.  We  well 
know  that  nearly  all  bodies  expand  or  swell  when  they 
are  heated ;  and  we  know  equally  well  that  they  shrivel 
or  contract  in  the  process  of  cooling.  Now,  where  the 
sxtremes  of  heat  and  cold  in  the  atmosphere  are  spe- 
cially great,  or  follow  one  another  in  quick  succession, 
the  rock,  in  adapting  itself  to  such  changes,  is  liable  to 
respond  with  insufficient  rapidity,  and  the  result  is  that 
it  splits  to  pieces.  Especially  is  this  the  case  in  desert 
regions,  where  the  heat  of  day  is  almost  intolerable,  and 
where  at  night  ice  often  forms.  Travellers  in  such 
regions  have  actually  seen  the  chips  fly,  and  more  often 
have  heard  them  crack. 

A  third  method  which  produces  decay  in  rocks  is  one 
that  cannot  be  watched  so  easily.  It  is  something  that 
goes  on  inside,  and  does  not  permit  its  doings  to  be  fol- 
lowed by  the  eye.  When  you  leave  a  knife  or  shovel 
out  of  doors  in  a  damp  night,  you  are  not  surprised  in 
the  morning  to  find  it  more  or  less  rusty.  Iron-rust  is 
merely  a  combination  of  the  metal  and  some  of  the  gas 
substance  of  the  atmosphere  known  as  oxygen ;  the 
two  have  united,  and  they  now  form  the  new  combina- 
tion. How  often  in  your  wanderings  through  a  city 
have  you  noticed  ugly  yellow  or  reddish  stains  on  the 


16  THE  EARTH  AND  ITS   STORY. 

surfaces  of  stately  marble  or  granite  buildings ;  white 
marble  doorsteps  and  window-sills  are  much  in  the 
same  way.  When  this  is  the  case,  the  fact  tells  us 
that  iron  has  rusted  within  the  rock,  and  perhaps  this 
is  the  first  suspicion  that  we  have  that  the  rock  con- 
tains iron.  There  are  within  the  rock  other  substances 
besides  iron  which  tend  to  take  in  the  oxygen  from  the 
atmosphere ;  they  also  "  oxygenate,"  or  burn,  or  rust, 
but  when  they  do  this  they  produce  changes  in  the 
rock,  and  these  changes  are  generally  in  the  direction 
of  decay.  New  combinations  are  formed,  and  old  ones' 
are  destroyed.  Hence,  geologists  say  that  one  of  the 
prime  agents  in  producing  decay  is  the  taking  in,  by 
the  rock,  of  oxygen  from  the  outside,  and  the  making 
of  new  chemical  combinations  within.  Our  second 
lesson  in  geology  teaches  us  that  rocks  crumble  or 
decay  in  two  ways  of  their  own,  mechanically  and 
chemically.  Hence  we  say  :  Rocks  undergo  mechanical 
and  chemical  destruction  or  disintegration. 

The  Weathering  of  Rocks.  —  I  often  sit  in  the  lonely 
little  graveyard  that  adjoins  the  country  parish  church, 
and  muse  over  those  quaint  inscriptions  on  the  tomb- 
stones which  tell  of  peaceful  deaths  in  years  gone  by. 
Some  record  the  years  1720  and  1725,  others  go  back 
a  half-century  or  more,  while  still  others  remind  us 
that  life  has  only  recently  departed.  I  notice,  too,  that 
some  of  the  oldest  inscriptions  are  seemingly  as  fresh 
as  though  they  had  been  cut  yesterday;  many  of  the 
newer  ones,  on  the  other  hand,  are  nearly  wiped  out, 
and  bear  the  rude  traces  that  weather  and  time  have 
worn  upon  them.  When  I  still  believed,  with  my  good 
fanner,  that  rocks  grew,  this  difference  in  the  inscrip- 


WHAT  THE  ROCKS  TEACH.          17 

tions  puzzled  me ;  but  knowing  now,  that,  instead  of 
growing,  all  rocks  break  away,  it  is  not  difficult  to 
account  for  the  difference.  Some  have  stood  the  in- 
fluences of  the  atmosphere  better  than  others  —  they 
have  weathered  more  lightly.  The  marks  may  be  older, 
but  they  have  stood  the  tests  of  time  more  firmly  than 
their  neighbors.  Who  has  not  at  one  place  or  another 
observed  how  differently  some  rocks  behave  before  the 
atmosphere  than  others ;  how  some  break  before  the 
pounding  surf  of  the  ocean  in  one  way,  and  some  in 
another?  These  peculiarities  are  a  part  of  the  struc- 
ture of  the  rock ;  they  are  born  with  it,  and  in  a  meas- 
ure shape  its  future  course.  Who  does  not  know  that 
some  rocks  when  they  break,  break  in  rounded  masses, 
that  others  break  in  sharp  and  angular  blocks,  and 
that  others  wear  away  with  smooth  and  flowing  lines  ? 
Whether  destroyed  in  one  way  or  another,  they,  to  use 
a  geological  expression,  "  weather  differently."  The 
finer  elements  of  scenery  —  the  rugged  cliffs  and  nee- 
dles, the  domes,  the  undulating  knolls  and  meadows  — 
are  largely  the  result  of  this  irregular  weathering ; 
that  is,  of  the  way  in  which  different  kinds  of  rock 
stand  exposure  to  the  assaults  of  decay  and  destruc- 
tion. Just  what  it  is  that  gives  to  different  rocks  their 
distinctive  methods  of  wearing  or  weathering  is  not 
always  clear ;  but  so  persistent  is  the  form  of  decay  for 
certain  classes  of  rock,  that  an  experienced  eye  can 
frequently  detect  the  rock  that  lies  ahead  of  him,  with- 
out having  first  seen  it,  from  the  contour  of  the  land- 
scape alone.  (Plates  1,  2,  13,  48,  and  49.) 

Desert  Sands  and  Deserts.  —  Only  a  few  years  ago 
it  was  a  common  belief  that  the  sands  of  the  desert 


18  THE  EARTH  AND  ITS   STORY. 

represented  an  old  ocean  bottom  which,  in  one  way  or 
another,  had  been  lifted  out  of  the  sea  and  made  dry  — 
or,  at  any  rate,  the  water  that  had  covered  it  had  been 
removed.  To-day  we  know  that  this  is  not  strictly  the 
case  ;  for  whether  the  region  had  ever  been  beneath  the 
sea  or  not,  the  sands  are  merely  the  decomposed  parts 
of  the  solid  rock  that  underlies  them.  The  desert,  in- 
deed, is  not  that  uniform  expanse  of  sand  which  per- 
haps most  persons  still  believe  it  to  be ;  but  it  shows 
ranges  of  rocky  hills  and  mountains  passing  through  it 
in  various  directions,  and  it  is  from  the  destruction  of 
these  that  the  sands  have  come  about.  They  are  just 
the  counterpart  of  the  dust  and  mud  on  the  highway. 
The  reason  that  we  have  so  much  sand  accumulated 
in  desert  regions  is  because  in  such  regions  there  is 
little  rain-fall  and  consequently  but  few  streams ;  neces- 
sarily, therefore,  the  sand  remains  where  it  was  formed, 
and  only  adds  itself  year  by  year  to  a  steadily  increas- 
ing quantity.  Were  there  a  sufficient  number  of 
streams  to  carry  it  away,  as  we  find  in  more  favored 
countries,  there  never  would  be  any  great  thickness  of 
it,  except  possibly  in  the  line  of  some  wind-drifts.  We 
never  have  very  much  dust  on  our  roadways,  because 
the  rains  and  streams  every  little  while  carry  away 
what  has  been  formed ;  but  we  do  find  that,  when  rain 
has  ceased  for  a  long  time,  the  quantity  of  dust  very 
materially  increases  during  the  period  of  drought.  We 
are  here  brought  face  to  face  with  an  important  lesson : 
The  materials  of  destruction  of  the  earth's  surface  are 
distributed  by  the  rain-waters  and  the  streams  resulting 
from  them. 

The  Course  of  Mud  and  Sand.  —  We  now  ask,  where 


WHAT  THE  ROCKS  TEACH.  19 

do  these  materials  go  ?  They  can  only  go  where  the 
streams  take  them,  and  by  far  the  greater  number 
leisurely  travel  to  the  sea.  A  few  there  are  which  dry 
out  or  lose  themselves  before  they  reach  the  sea ;  and 
a  few  discharge  into  lakes  or  interior  seas  which  possi- 
bly have  no  outlet.  In  such  cases  the  materials  which 
they  carry  are  dropped  along  the  route  of  their  journey, 
some  of  it  distributed  here,  some  of  it  elsewhere.  In 
lakes  they  help  to  build  up  the  bottom ;  on  plains  and 
meadows  they  help  to  raise  the  surface.  But  by  far 
the  greatest  quantity  of  the  material  follows  the  large 
rivers  to  the  ocean,  and  there  it  is  dropped ;  what  be- 
comes of  it  after  that  we  shall  find  out  later  on.  Thus 
it  is  that,  seeing  all  parts  of  the  earth's  surface  under- 
going destruction  and  being  carried  ocean  ward  by  the 
numerous  rivers,  we  frequently  say,  "the  earth  is  on 
one  grand  march  to  the  sea." 


20  THE  EARTH  AND  ITS   STOBT. 


CHAPTER   II. 

SOME  OF  OUR  COMMONER  ROCKS,  AND  HOW  THEY 
ARE  MADE. 

Sandstone  is  one  of  the  commonest  of  rocks,  and 
it  is  to  be  found  almost  everywhere.  In  our  large 
cities,  like  New  York,  Chicago,  Philadelphia,  and  Bos- 
ton, it  is  much  used  as  building-stone,  and  makes  up 
what  is  familiar  to  us  as  "brownstone"  and  "gray- 
stone  fronts."  It  may  be  brown,  red,  yellow,  white, 
or,  in  fact,  almost  any  color ;  and  of  whatever  color, 
it  hardly  differs  in  structure.  If  you  run  your  eye 
closely  over  the  specimen  that  has  just  been  obtained  at 
the  stone-yard,  you  will  note  that  where  freshly  broken, 
it  is  a  rough  rock,  and  that  this  roughness  is  in  the 
main  due  to  innumerable  glassy  particles  which  come 
to  the  surface.  You  will  immediately  recognize  these 
particles  to  be  the  same  as  the  sands  of  the  sea-shore. 
Scratched  with  a  knife,  the  rock  gives  out  a  hard  grat- 
ing sound,  which  shows  its  toughness  ;  a  tiny  piece  put 
between  the  teeth  makes  them  grit  in  the  same  way 
that  sea-sand  would  were  it  put  in  the  same  position. 

However  plainly  sandstone  shows  itself  to  be  built 
up  of  innumerable  sand  particles  or  grains,  it  does  not 
so  clearly  teach  us  how  these  grains  are  united  together 
to  form  a  compact  rock.  Sometimes,  through  hard 
pressure,  especially  where  we  are  assisted  by  moisture 


Plate  3. 


*§*•   LA     ^t*    Jau^-J^        *  <'*  -.-.     '     -  :- «      -jf#-      "        ^^'d> 

^'•Jf^/w-/^  •  -\  f^  ^-v  ''"';i  ''« v'  "%?• 

-,Jjfe^.^fv.V V.^*:';r . '  ^> 


*.„ 


S3. 

1.  A  piece  of  granite:  the  dark  spots  are  black  mica;  the  gray  areas  are  quartz,  and 

the  white,  feldspar. 

2.  A  piece  of  gneiss,  showing  a  V-shaped  fold,  and  the  foliated  structure  of  the  rock. 


Plate  4. 


1.  A  piece  of  pudding-stone,  or  conglomerate.    2.  Apiece  of  shell-rock,  coquina.    3=  A 
fragment  of  crinoidal  limestone,  showing  fragments  of  crinoid  stems. 


HOW  COMMONER   ROCKS  ARE  MADE.  21 

of  some  kind,  we  can  make  loose  particles  not  only 
stick  together,  but  hold  together  for  an  almost  in- 
definite time.  We  have  all  observed  how  the  salt  on 
our  tables  is  "  lumped  "  by  the  spoon  being  put  into 
it  too  frequently,  or  how  the  loose  earth  of  our  back 
yards,  with  the  addition  of  a  little  water,  can  be 
"patted"  out  into  movable  bricks.  Nature  does  an 
enormous  amount  of  patting  and  pressing,  as  we  shall 
learn  further  on;  and,  doubtless,  many  of  the  solid 
rocks  of  the  earth  have  been  built  up  firm  from  loose 
particles  through  long-continued  compression  alone. 
The  recognition  of  this  fact  is  an  important  step 
towards  understanding  what  a  rock  really  is,  and  how 
it  does  not  materially  differ  from  the  loose  materials 
that  everywhere  surround  us.  Indeed,  geologists  fre- 
quently speak  of  loose  sands,  of  clays,  and  even  of 
water,  as  rocks. 

Pebble-Rocks  or  Conglomerates  ("  Pudding-Stones  "). 
The  other  day  I  received  from  a  genial  sea-captain 
of  our  coast  a  ship's  bolt  which  had  been  buried  in  the 
sea  for  about  twelve  years ;  the  good  ship  to  which  it 
belonged  had  gone  to  the  bottom  by  striking  a  pebbly 
shoal',  and  its  materials  were  lying  scattered  about  be- 
neath the  angry  waters.  There  was  little  strange  about 
the  bolt  itself,  which  was  badly  rusted,  but  completely 
sheathing  it  for  a  length  of  some  twenty  inches  or  more 
was  a  case  of  small  yellow  and  red  stained  pebbles.  I 
could  draw  the  bolt  in  and  out  of  its  case,  just  as  you 
can  draw  a  sabre  from  its  sheath.  It  was  plain  that 
the  pebbles  had  been  united  to  one  another  through 
iron-rust,  which  acted  first  as  a  soft  cement  and  then 
hardened ;  and  this  work  of  building  up  a  solid  rock 


22  THE  EARTH  AND   ITS   STORY. 

of  loose  pebbles  was  accomplished  in  a  period  of  twelve 
years. 

Country  folks  frequently  speak  of  a  rock  common  in 
their  region  as  "pudding-stone,"  so  called  from  a  fan- 
cied resemblance  of  the  rock  to  plum-pudding;  it  is 
made  up  of  innumerable  pebbles,  the  "plums,"  which 
are  held  together  much  in  the  way  of  the  pebbles  of  my 
bolt-sheath.  To  the  geologist  such  a  pudding-stone  is 
known  as  conglomerate,  and  he  recognizes  in  it  a  vast 
association,  or  conglomeration,  of  rolled  rock-fragments, 
the  pebbles,  which  have  united  to  form  a  compact  rock. 
And  oftentimes  this  rock  extends  for  miles  across 
the  country,  and  measures  hundreds  of  feet  in  thick- 
ness. It  is  not  iron-rust  alone  that  acts  as  a  cement; 
more  often,  perhaps,  it  is  a  lime-paste,  or  the  substance 
of  limestone  and  marble  dissolved  in  water.  Many 
waters  hold  this  substance  in  solution,  and  invisibly, 
until  for  some  reason  or  another  it  is  dropped  out,  or 
"precipitated"  as  geologists  say.  (Plate  4,  Fig.  1.) 

Where  the  Materials  of  Sandstone  come  from.  —  The 
study  of  a  piece  of  sandstone  teaches  us,  apart  from 
what  the  rock  itself  is,  how  loose  materials  may  be  and 
are  compacted  into  a  hard  rock:  by  compression,  by 
chemical  union  (as  in  the  case  of  iron-rust  and  lime 
bindings),  and  by  the  combination  of  the  two.  The 
sandstone  itself  is  a  union  of  particles  or  grains  of 
(quartz)  sand,  generally  held  together  in  one  of  the 
methods  here  indicated.  It  may  be  fine  grained  or 
coarser  grained,  as  are  many  of  the  millstones  (the  so- 
called  "grits"),  and  from  the  latter  we  easily  pass 
to  the  pebbly  conglomerates  or  pudding-stones.  We 
have  not  yet  asked  ourselves  the  question:  Whence 


HOW  COMMONER  ROCKS  ARE  MADE.  23 

come  the  sands  which  make  up  sandstones,  whence 
come  the  pebbles  that  make  up  pudding-stones  ?  You 
have  frequently  walked  over  them  in  your  quiet  ram- 
bles on  the  sea-shore ;  but  perhaps  the  thought  never 
entered  your  mind  that  the  beautiful  strand  which 
catches  the  falling  waters,  whether  of  sand  or  of 
shingle  (pebble),  is  the  substance  of  possible  future 
rocks.  It  has  been  brought  where  it  is  from  the  break- 
ing up  of  other  rocks,  the  same  that  my  farmer  friend 
assured  me  grew  on  his  meadow.  The  rocks  of  the 
land  break  up,  their  parts  are  distributed  by  the  differ- 
ent streams,  and  in  the  main  carried  to  the  sea ;  and  in 
or  along  the  sea  they  are  again  prepared  for  new  rock- 
making.  It  is  there  that  one  could  almost  say  rocks 
grew,  but  the  growing  is  very  different  from  what  we 
habitually  understand  by  that  term. 

Our  sandstone  is  then  of  marine  origin,  since  it  is 
made  up  of  the  oceanic  sands ;  and  these  sands  must 
have  been  derived  from  the  destruction  of  such  rocks  as 
contained  the  elements  of  true  sand,  possibly  some  more 
ancient  sandstones,  or  even  granites.  In  stating  that 
it  is  of  marine  origin,  we  only  say  what  is  true  of  by 
far  the  greater  number  of  rocks  of  the  earth.  It  is  a 
fact  that  some  (and  even  sandstones)  have  been  formed 
in  the  fresh-waters  of  the  land,  in  lake-basins,  and  in 
river  courses  ;  such  are  designated  "  fresh-water  rocks  " 
(fresh-water  sandstones,  etc.).  We  shall  learn  later 
how  to  distinguish  between  the  two  classes. 

Limestones  and  Marbles.  —  Hardly  less  common  than 
sandstone,  and  in  many  places  much  more  abundant 
than  it,  are  the  limestones.  Marble,  which  is  only  a 
crystalline  form  of  limestone,  is  known  to  us  all  in  the 


24  THE  EARTH  AND  ITS   STORY. 

many  marble  buildings  of  our  cities,  in  the  white,  yel- 
low, red,  blue,  and  black  mantels  of  our  parlors,  in 
table-tops,  front-door  steps,  window-sills,  etc.  A  piece 
'of  limestone  or  marble  examined  in  the  manner  of  our 
sandstone  sho^s  it  to  be  a  much  softer  rock;  it  cuts 
readily  with  a  knife,  without  a  grating  sound ;  and  if 
a  chip  is  placed  between  the  teeth  it  can  be  easily, 
powdered  up,  and  there  is  none  of  that  unpleasant 
gritty  feel  which  we  have  associated  with  the  biting 
of  sandstone.  Some  forms  of  limestone  are,  in  fact, 
naturally  "powdery;  "  such  is  common  chalk. 

In  all  three  the  substance  is  a  chemical  combination 
of  carbonic-acid  —  the  gas  which  is  familiar  to  you  in 
the  fizz  of  soda-water  —  and  lime.  Put  a  little  of  your 
material  in  some  strong  acid,  and  you  will  presently 
note  tiny  bubbles  rising  to  the  surface ;  these  are  bub- 
bles of  carbonic-acid  gas,  which  have  been  liberated 
through  the  action  of  the  stronger  acid.  Your  rock 
has  been  broken  up  ("dissociated")  by  the  action  of 
the  acid ;  a  part  of  it  has  disappeared  as  gas,  while  the 
rest,  the  lime,  has  been  taken  up  in  solution  by  the 
liquid  acid  itself.  Were  we  to  apply  the  same  test  to 
the  shells  of  the  oyster,  the  clam,  the  snail,  or  the  deli- 
cate tracery  of  coral  which  rests  on  our  mantel,  we 
should  obtain  a  like  result ;  for,  in  fact,  their  substance 
is  the  substance  of  limestone  and  marble,  and  nothing 
more.  How  often  have  you  looked  at  a  polished  marble 
table-top,  or  at  a  mantel,  and  remarked  the  curious 
figures  which  appear  at  the  surface,  and  immediately 
suggest  to  you  the  shells  of  the  sea-shore  !  Not  know- 
ing how  limestone  or  marble  is  made  up,  many  people 
believe  these  marks  or  figures  to  be  the  design  of  the 


HOW  COMMONER   BOCKS  ARE  MADE.  25 

builder  or  stone-cutter;  but  they  are  true  shells,  which 
ages  ago  belonged  to  living  animals,  and  the  whole 
mass  together  constitutes  a  shelly  limestone.  Many  of 
the  table-tops,  more  particularly  in  England,  show 
plainly  the  impressions  of  corals,  and  hardly  anything 
else ;  such  are  coral  limestones.  And  there  are  many 
that  are  crammed  full  of  the  parts  of  a  class  of  animals, 
distantly  related  to  the  starfishes,  which  are  known  as 
stone-lilies  or  crinoids ;  they  were,  in  past  ages  of  the 
earth's  history,  exceedingly  abundant,  but  to-day  only 
linger  on.  Limestones  made  up  of  these  parts  are 
known  as  crinoidal  limestones.  (Plate  4,  Fig.  3.) 

Organic  Nature  of  Limestones.  —  From  the  facts  that 
we  have  here  learned,  the  suspicion  grows  upon  us 
that  limestone  or  marble,  no  matter  how  it  appears,  — 
whether  it  shows  the  marks  of  animal  existence  or  not, 
-  is  principally  a  make-up  of  the  hard  parts  of  various 
shell-fish,  corals,  etc.,  which  lived  at  about  the  time 
that  the  rock  was  being  formed.  And  so  it  really  is. 
It  was  only  the  other  day  that,  in  one  of  our  large  cities, 
standing  at  the  intersection  of  two  streets  in  front  of  a 
row  of  houses  that  were  then  building,  I  noticed  that 
the  lower  course  of  stone  was  of  an  unusually  attrac- 
tive bluish  color ;  stepping  up  to  it  for  a  nearer  study, 
I  found,  to  my  pleasure,  that  the  whole  mass  was  one 
dense  accumulation  of  minute  shells,  corals  and  coral- 
lines, some  of  them  so  tiny  that  only  with  a  strong 
pocket  magnifier  could  the  parts  be  clearly  distin- 
guished. They  stood  out  in  all  directions,  for  the 
rock  was  rough-dressed,  and  not  polished.  In.  a  cubic 
foot  of  the  rock  there  must  have  been  hundreds  of 
thousands,  perhaps  millions,  of  these  ancient  or  fossil 


26  THE  EARTH  AND  ITS   STORT. 

remains.  For  one  who  had  never  seen  anything  of 
the  kind  before,  there  could  be  no  more  impressive 
lesson  —  to  think  of  the  billions  and  billions  of  life- 
forms  that  go  to  build  up  limestone  rock! 

The  Obliteration  of  Organic  Traces.  —  Unfortunately 
it  is  not  in  all  limestones  that  we  can  distinguish 
the  organic  parts  which  enter  into  their  construction. 
In  some,  these  parts  are  so  minute  that  they  readily 
escape  the  eye;  in  others,  only  the  microscope  can 
determine  their  presence ;  and  in  still  others,  the  micro- 
scope, as  well  as  the  unassisted  eye,  fails  to  make  out 
anything.  In  many  such  cases,  and  probably  in  the 
greater  number  of  them,  we  are  right  in  assuming  that 
the  animal  traces  did  at  one  time  exist ;  but,  in  the 
long  course  of  changes  through  which  the  rock  has 
passed  since  it  was  first  formed,  the  marks  have  be- 
come obliterated.  Just  as  in  the  living  animal  the 
life  can  be  crushed  out  of  it,  so  with  these  harder 
parts,  they  have  been  crushed  out  of  recognition. 
The  pressures  to  which  the  rock  has  been  subjected, 
the  chemical  and  physical  changes  that  have  taken 
place  within  it,  have  been  sufficient  to  destroy  the 
final  traces.  Probably  by  far  the  greater  part  of  the 
massive  limestones  and  marbles  which  crop  out  in  our 
quarries,  which  make  up  giant  mountains,  has  been 
built  up  by  inhabitants  of  the  sea,  —  the  shell-fish, 
corals,  etc.  Strange  as  this  may  sound,  it  yet  appears 
to  be  the  case;  and  if  it  is  true,  then  wherever  we 
have  marine  limestones  to-day  we  have  had  the  sea  at 
an  earlier  day  occupying  the  same  position. 

Coquina  Rock.  —  Most  limestones  have  in  their  con- 
jstruction,  in  addition  to  the  animal  parts  which  strictly 


COMMONER   HOCKS  AEE  MADE.  27 

build  them  up,  a  binding  cement  of  lime.  Along  the 
sea-shore,  where  shells  are  plentiful,  we  not  infre- 
quently find  a  number  of  these  stuck  together,  and 
so  firmly  that  it  is  impossible  to  separate  them  without 
breaking.  There  is  no  more  interesting  rock  than  that 
which  is  to-day  forming  along  the  Florida  coast  —  the 
so-called  coquina ;  it  is  used  in  the  construction  of 
many  of  the  southern  buildings,  especially  of  the 
humbler  kinds,  and  consists  of  coarse  shell  fragments, 
held  together  by  nature's  cement,  the  carbonate  of 
lime.  It  shows  so  plainly  how  it  is  made  up,  that  it 
reads  for  itself  a  complete  chapter  in  limestone  con- 
struction. (Plate  4,  Fig.  2.) 

Fresh-water  limestones  are  not  very  generally  of 
great  extent.  They  are  built  up  of  the  shells  of 
animals  that  inhabit  the  fresh  waters,  lakes  and  rivers^- 
and  whose  forms  it  is  not  difficult  to  distinguish  from' 
those  which  belong  to  the  waters  of  the  ocean.  In  a 
subsequent  lesson  we  shall  study  another  type  of  lime- 
stones,—  the  stalactites  and  stalagmites  of  caves. 

Chalk.  —  This  material  does  not  differ  greatly  from 
ordinary  fine-grained  limestones,  except  that  it  is  soft 
and  powdery,  and  for  this  reason  well  adapts  itself  to 
writing  purposes.  It  is  of  the  class  which  geologists 
frequently  designate  as  "earthy  limestones,"  and  before 
an  acid  it  behaves  like  almost  every  other  form  of  lime- 
stone, It  was  a  happy  inspiration  which  prompted  a 
distinguished  naturalist  to  put  a  morsel  of  it,  well 
powdered,  in  the  field  of  his  microscope :  he  saw  the 
greater  part  of  the  mass  broken  up  into  a  multitude 
of  tiny  shells,  some  of  them  so  minute  as  entirely  to 
escape  detection  by  the  naked  eye.  Some  of  them, 


28  THE  EARTH  AND   ITS   STORY. 

again,  were  about  the  size  of  a  grain  of  pepper;  others 
perhaps  of  the  size  of  a  pin's  head,  and  not  many 
larger.  They  are  all  of  them  remains  of  very  nearly 
the  lowliest  of  organisms  —  organisms  which,  while 
they  have  hard  parts,  are  practically  destitute  of  organs. 
They  have  no  blood  system,  no  nerve  system,  and  no 
true  muscular  system.  They  have  neither  head  nor 
stomach,  nor  any  internal  support  of  any  kind.  But, 
despite  these  deficiencies,  they  grow  on,  develop,  and 
reproduce  like  all  other  animals,  except  in  a  somewhat 
different  manner,  and  seemingly  go  through  the  entire 
cycle  of  existence.  Naturalists  call  them  Foraminifera, 
meaning  pore-bearers,  from  the  number  of  minute  open- 
ings or  pores  which  their  shells  contain.  Through  these 
openings,  in  the  living  state,  the  animal  protrudes  deli- 
cate processes  of  the  body,  which  help  to  propel  it 
about,  and  probably  bring  to  it  a  certain  amount  of  its 
food  supply. 

Oceanic  Ooze  ;  Globigerina  Ooze.  —  For  our  present 
purposes  it  is  sufficient  to  know  that,  with  one  or  two 
exceptions,  all  the  animals  of  this  class  to-day  inhabit 
the  ocean,  where  they  are  so  numerous,  especially  the 
kind  known  as  G-lobigerina  (the  "  globe-bearer "),  that 
their  dead  shells,  falling  to  the  bottom,  make  the  greater 
part  of  a  whitish  or  gray  mud-paste  which  is  forming 
there.  This  Globigerina  mud,  or  "ooze,"  which  con- 
tains parts  of  many  other  animals,  such  as  the  teeth 
of  sharks,  the  bones  of  whales,  etc.,  follows  the  floor  of 
the  sea  to  a  depth  of  about  15,000  feet;  it  has  been 
accumulating  through  a  long  period,  and  how  thick  or 
how  deep  it  is,  nobody  knows.  It  so  happens  that  just 
this  form  of  Globigerina  is  also  about  the  most  abun- 


HOW  COMMONER   ROCKS  ARE  MADE.  29 


dant  of  the  organisms  in  chalk  r^fliSfefore,  from  this 
and  a  number  of  other  circumstances,  we  conclude  that 
the  great  chalk  deposits  of  the  globe,  like  those  which 
extend  almost  continuously  from  the  picturesque  white 
cliffs  of  England  and  France  to  and  through  Russia, 
represent  an  ancient  sea-bottom  very  much  like  that 
which  is  found  to-day  in  the  deep  ocean,  —  perhaps  not 
extending  to  quite  12,000  or  15,000  feet,  but  almost 
certainly  to  6,000  or  8,000  feet. 

When  we  speak  of  chalk,  we  refer  to  the  article  that 
is  fresh  from  the  chalk  cliffs,  and  not  to  the  scratchy 
substance  which  so  frequently  and  so  obstinately  de- 
clines to  leave  its  mark  on  the  blackboard.  Many  of 
our  "chalk"  sticks  are  only  a  cheap  artificial  compound 
of  sulphuric  acid  and  lime,  —  a  spurious  gypsum. 

Flags,  Shales,  and  Slates.  —  We  often  find  that  the 
sticky  and  disagreeable  mud-flats  of  the  ocean  front, 
which  perhaps  follow  the  sands  and  pebbles,  "  cake  " 
hard  in  dry  or  hot  weather.  Frequently  have  we  at- 
tempted to  cross  one,  perhaps  for  no  other  purpose  than 
to  see  how  well  it  would  stand  our  weight;  and  often 
have  we  exclaimed  that  it  was  as  "hard  as  a  rock." 
When  we  said  this,  we  were  saying  something  that  was 
not  far  from  the  truth ;  for,  in  fact,  this  same  mud  is 
making  rock.  Hundreds  of  thousands  of  feet  in  thick- 
ness of  rock  that  appears  in  our  quarries  and  in  the 
mountain  sides  are  merely  compacted  muds,  —  the  sea- 
fronts  or  sea-bottoms  of  ancient  times.  Such  is  the 
greater  number  of  the  gray  and  blue  flagging  stones  of 
our  street  sidewalks,  the  black  writing-slates,  the  green, 
red,  and  black  roofing  tile-stones,  etc.  Some  of  these 
rocks  are  known  to  the  geologist  as  shales,  because  they 


30  THE  EARTH  AND  ITS   STORY. 

shale  off  in  slabs  of  regular  and  not  very  great  thick- 
ness ;  it  is  to  the  thinner  plates  that  the  name  of 
slate  is  given.  So  perfectly  have  the  old  ocean  muds 
retained  their  original  characters,  that  on  many  of  them 
we  still  see  the  ripple-marks  which  were  carved  on 
them  when  they  were  yet  a  part  of  the  beach;  others 
have  sun-cracks,  and  some  the  pits  which  were  im- 
pressed into  them  by  the  falling  drops  of  rain.  Here 
and  there  we  can  trace  the  burrow  of  the  ancient  worm, 
or  the  tracery  which  has  been  left  by  the  decaying  sea- 
weed. And  yet  all  these  marks  and  impressions  may 
belong  to  a  period  removed  millions  of  years  from  us ! 

The  muds  are  brought  to  the  ocean  principally  in  the 
discharge  of  the  great  rivers,  —  rivers  whose  basins 
cover  much  disintegrated  rock,  and  where  there  is  a 
good  supply  of  loose  soil.  Indeed,  soil  is  frequently 
decomposed  shale  and  flag,  the  hard  rock  once  more 
going  back  to  the  condition  of  mud.  Elsewhere  it  is 
formed  from  the  destruction  of  several  other  kinds  of 
rock,  the  granites,  sandstones,  etc. 

Granite.  —  Of  the  many  useful  rocks  that  are  em- 
ployed in  the  arts,  none  perhaps  is  more  useful  than 
granite,  and  there  is  none  that  equals  it  in  beauty. 
From  the  most  ancient  times  to  the  present  it  has  been 
considered  preeminently  the  building-stone ;  and  if  it 
has  its  defects,  it  has  certain  good  qualities  which  no 
other  rock  has.  Some  people  know  granite  only  when 
it  is  gray,  others  only  when  it  is  red ;  and  they  seem  to 
be  ignorant  of  the  fact  that  it  can  be  of  almost  any 
color,  the  color  depending  chiefly  upon  the  character- 
istics of  one  of  its  several  constituents. 

Take  up  the  first  piece  of  really  good  granite  that 


SOW  COMMONER   HOCKS   ARE  MADE.  31? 

you  come  across,  and  examine  it.  You  find  it  to  be 
a  coarse-grained  rock,  with  particles  which  it  is  not 
difficult  to  recognize  as  belonging  to  at  least  three  dis- 
tinct mineral  species.  One  of  these  is  familiar  to 
everyone  as  mica,  the  mineral  that '  is  often  wrongly 
called  "  isinglass."  It  occurs  in  gray  or  blackish 
shining  plates,  which  the  blade  of  a  knife  can  easily 
separate  into  thin  seams.  Wherever  granite  occurs  in 
the  field,  particles  of  this  shining  silvery  mineral  will 
be  found  scattered  about  in  the  dust  or  sand,  particles 
from  the  rock's  disintegration. 

A  second  mineral  in  granite  is  the  gray  or  bluish 
quartz ;  it  has  a  dull,  glassy  appearance,  cannot  be 
scratched  with  the  knife,  and  always  breaks  across 
with  irregular  surfaces.  It  is  the  substance  which  we 
have  already  learned  to  recognize  in  sea-sand ;  and  from 
it,  indeed,  much  of  the  sea-sand  is  derived.  The  third 
mineral  constituent,  known  as  feldspar,  is  that  which 
generally  determines  the  color  of  the  granite ;  it  may  of 
itself  be  green,  yellow,  blue,  or  red,  and  as  such  it  may 
give  these  colors  to  the  rock.  Otherwise  in  most  cases 
it  can  easily  be  distinguished  from  quartz  by  its  pearly 
lustre,  by  being  somewhat  scratchable  with  the  knife, 
and  by  breaking  more  nearly  in  flattened  surfaces. 
With  these  three  substances  in  its  composition,  a 
typical  granite  is  built  up.  (Plate  3,  Fig.  1.) 

Distinct  Types  of  Granite.  —  There  are  granites  which 
contain  certain  additional  minerals  scattered  about  in 
their  mass,  —  thus,  tourmaline  granite  contains  the  min- 
eral tourmaline ;  garnetiferous  granite,  the  mineral  famil- 
iar to  all  as  garnet,  and  so  forth.  But  these  do  not 
concern  us  at  this  time.  One  mineral  there  is,  how- 


32  THE  EAETH  AND   ITS   STORY. 

ever,  which  is  so  often  and  so  closely  associated  with 
the  quartz,  feldspar,  and  mica  in  the  granite  as  to  make 
it  almost  as  much  a  part  of  the  rock  as  the  rest ;  this 
is  the  black  or  greenish-Hack  hornblende,  small  flakes 
of  which  are  often  mistaken  for  black  mica.  Its  great 
hardness,  and  the  fact  that  it  does  not  separate  into 
thin  sheets,  ought  readily  to  distinguish  it.  When  the 
hornblende  is  present  in  large  quantities,  it  makes  Jiorn- 
blendic  granite.  At  times  it  not  only  replaces  the  mica, 
but  also  the  quartz ;  the  granitic  rock  is  then  generally 
known  as  syenite.  But  whether  syenite,  hornblendic 
granite,  or  granite  proper,  the  rock  has  much  the  same 
habit.  It  is  a  crystalline  or  semi-crystalline  aggrega- 
tion of  mineral  particles,  which  may  be  either  coarsely 
large  or  minutely  fine,  making  coarse-grained,  fine- 
grained, and  intermediate-grained  granites.  Sometimes 
the  individual  elements  may  be  several  inches  across,  at 
other  times  they  are  so  minute  as  to  be  barely  recogni- 
zable by  the  unassisted  eye.  In  one  class  of  granites  the 
feldspars  have  the  form  of  true  crystals,  and  some  of 
these  are  scattered  about  with  more  or  less  regularity 
through  the  rock.  Such  granites  are  known  as  porphy- 
ritic  granites,  or  simply  as  porphyries. 

Origin  of  Granite.— -  The  fact  has  long  been  known 
that  the  cores  or  deep  interiors  of  many  of  the  biggest 
mountains  are  constituted  of  granite ;  hence  this  rock 
has  frequently  been  looked  upon  as  the  foundation- 
stone  of  the  earth.  It  has  been  supposed  to  be  the 
oldest  of  all  rocks,  to  have  been  the  first  to  form  when 
the  earth  was  still  in  a  semi-gaseous  or  half  nebulous 
condition,  and  to  have  formed  through  the  action  of 
intense  heat  and  under  great  pressure.  Just  how  it 


HOW  COMMONER   KOCKS  ABE  MADE.  33 

was  made  no  one  could  know,  and  not  much  more  do 
we  know  to-day.  There  is  one  fact,  however,  which 
appears  to  be  almost  certain;  and  that  is,  that  in  the 
making  of  most  granites  a  very  high  degree  of  heat  was 
largely  concerned.  In  the  early  period  of  the  earth's 
history  there  was  such  a  heat,  and  it  is  perhaps  not 
surprising  that  so  much  of  the  granite  should  belong 
to  this  ancient  time.  But  even  to-day,  from  the  molten 
material  that  is  thrown  out  by  volcanoes,  granite  is 
sometimes  formed,  so  that  we  have  the  evidence  before 
us  of  how  at  least  some  of  the  rock  is  made. 

Igneous  and  Aqueous  Rocks  ;  Plutonic  Rocks.  —  The 
fact  that  some  rocks  require  for  their  making  the  action 
of  heat,  while  others  need  water,  has  led  geologists  to 
subdivide  the  entire  series  into  two  great  classes,  —  the 
igneous  rocks  and  the  aqueous  rocks.  Granite  and  its 
allies  belong  to  the  first  series,  and  the  sandstones,  lime- 
stones, and  shales  to  the  latter.  Again,  for  convenience, 
we  often  subdivide  the  igneous  rocks  themselves  into 
two  series,  —  such  as  solidify  on  cooling  from  a  molten 
condition  on  the  free  surface  of  the  earth,  like  the  lavas 
of  volcanoes ;  and  others  which  harden  under  pressure 
within  the  earth's  interior,  like  the  granites.  The  for- 
mer are  designated  igneous  rocks  proper,  and  the  latter, 
from  their  sharing  the  realm  of  the  Roman  god  Pluto, 
plutonic. 

Gneiss.  —  There  is  a  rock  which  in  many  ways  so 
nearly  resembles,  and  has  so  much  the  habit  of  granite, 
that  by  persons  who  are  not  geologists  it  is  frequently 
mistaken  for  it.  I  well  remember  how,  in  my  younger 
days  of  studentship,  I  was  puzzled  to  tell  this  gneiss 
from  granite ;  and,  if  candor  compels  me  to  tell  the  truth, 


84'  .        THR  EARTH  AND  ITS  STOUT. 

my  mind  even  to-day  is  not  always  free  in  its  judgment. 
Both  rocks  have  generally  identical  mineral  constituents, 
and  both  have  very  nearly  the  same  chemical  constitu- 
tion. An  easily  discerned  difference  can  be  found  only 
in  what  might  be  called  "  typical "  gneiss ;  there  it  will 
be  seen  that  the  different  mineral  species  of  the  rock,  — 
quartz,  feldspar,  and  mica  (or  hornblende  in  place  of 
mica),  —  instead  of  being  promiscuously  thrown  about 
in  their  arrangement,  are  disposed  in  more  or  less  regu- 
lar lines  or  bands,  which  give  a  "  foliated  "  (and  not  a 
"granitic")  appearance  to  the  mass.  Here,  so  far  as 
distinction  is  concerned,  we  are  on  safe  ground.  Often- 
times, however,  the  banding  or  foliation  becomes  ob- 
scured and  irregular,  and  we  approach  more  and  more 
the  structure  that  belongs  to  granite.  Finally  we  reach 
the  point  where  it  becomes  all  but  impossible  to  distin- 
guish between  the  two,  and  where  one  might  with  equal 
propriety  speak  of  a  granite  as  of  a  gneiss.  (Plate  3, 
Fig.  2.) 

Origin  of  Gneiss.  —  Long  before  the  days  of  my  geo- 
logical apprenticeship  the  masters  of  the  science  had 
discussed  the  possible  origin  and  method  of  formation  of 
gneiss,  and  the  discussion  continues  to  this  day.  Some 
have  argued,  as  concerning  granite,  that  it  was  the 
foundation-stone  of  the  earth;  others,  that  it  was 
merely  an  oceanic  mud  like  our  shales,  which,  through 
some  chemico-physical  action,  had  been  transformed  or 
metamorphosed  into  the  peculiar  rock  which  we  recog- 
nize to-day.  Volumes  have  been  filled  with  eloquent 
dissertations  on  this  subject,  volumes  will  probably  be 
filled  in  the  same  way  in  the  future ;  but  at  present 
almost  all  that  we  can  say  with  an  approach  to  cer- 


HOW   COMMONER   ROCKS  ARE  MADE.  35 

tainty  is,  that  gneiss  is  generally  —  almost  invariably  — 
a  very  ancient  rock,  and  perhaps  no  longer  made ;  it 
has  often  the  habit  of  granite,  into  which  it  seems  to 
pass  by  insensible  gradations ;  it  has  often  the  habit 
of  the  ordinary  aqueous  rocks,  of  which  it  may  be  only 
a  physical  or  chemical  transformation  or  metamorphism 
(hence  metamorphic  rock). 

It  occurs  in  masses  thousands  of  feet  in  thickness, 
and  generally  represents  the  most  ancient  parts  of  the 
continents  that  have  been  preserved  to  us. 

Mica  Schists  and  other  Schists.  —  In  some  rocks 
that  resemble  gneiss  the  mica  element  is  so  largely 
developed  that  it  gives  to  them  their  distinctive  char- 
acter. The  mineral  itself  occurs  in  fairly  large  plates ; 
and  these,  by  their  ready  division,  tend  to  "  schist,"  or 
break  the  rock  into  thin  plates  —  schists.  Hence  the 
rock  is  known  as  mica  schist;  generally  it  is  only 
an  alternation  of  quartz  particles  and  mica  scales  or 
plates.  Other  rocks  breaking  in  much  the  same  way, 
but  with  different  minerals  supplanting  the  mica,  are 
the  chlorite-schists,  hornblende-schists,  etc.  Much  of  the 
obscurity  which  still  attaches  to  the  origin  of  gneiss 
also  belongs  to  mica  schist;  and  the  two  are  not  only 
closely  associated  with  one  another,  but  seemingly  very 
closely  interrelated. 


36  THE  EARTH  AND  ITS   STORY. 


CHAPTER    III. 

"WHAT    ROCKS    LOOK    LIKE    DST    THE    FIELD. 

ONE  often  hears  the  remark :  I  should  like  to  study 
geology  if  I  only  knew  how  to  tell  the  rocks.  This  is 
not  a  difficult  task,  for  the  kinds  of  rocks  that  one 
ordinarily  meets  with  are  not  numerous.  We  have 
described  the  greater  number,  and  many  others  are 
merely  important  varieties  or  close  neighbors  of  these. 
So  far  as  distinguishing  them  is  concerned,  we  have 
only  to  find  out  to  what  broad  group  a  given  specimen 
belongs  through  a  common-sense  analysis.  /For  ex- 
ample, a  limestone  is  a  moderately  hard  rock,  which 
can  be  easily  scratched  or  cut  with  the  sharp  edge  of 
a  knife,  and  which,  when  particles  of  it  are  put  in  a 
strong  acid  (nitric,  sulphuric,  etc.),  gives  out  tiny 
bubbles  of  gas,  and  disappears.  If  a  cold  acid  will  not 
produce  this  effect,  the  acid  warmed  up  almost  invari- 
ably will.  Marble  acts  like  limestone,  and  only  differs 
from  it  in  having  its  mass  crystalline  or  sub-crystalline 
in  appearance  and  structure. 

A  shale  or  flag  is  also  a  rock  of  moderate  hardness, 
which  is  sometimes  not  easily  distinguishable  from  lime- 
stone ;  but  it  does  not  give  the  acid  test  (that  is  to  say, 
it  does  not  "effervesce").  The  difference  is  thus 
clear.  Occasionally  it  holds  lime  within  it,  and  then 
bubbles  of  gas  are  given  off ;  but  the  process  is  a  feeble 


WHAT  ROCKS   LOOK  LIKE  IN   THE  FIELD.        37 

one  as  compared  with  the  action  on  limestones.  Every- 
one knows  slate ;  it  is  a  thin  shale,  as  is  also  natural 
roofing-tile  or  tile-stone. 

A  sandstone  can  be  recognized  easily  by  its  granular 
or  grainy  structure,  the  irregular  sand  particles,  large 
or  small,  coming  roughly  to  the  surface.  It  is  a  rock 
that  scratches  hard,  and  gives  out  a  harsh  grating 
sound  when  the  knife-blade  is  pulled  across  it.  Acid 
has  little  or  no  effect  upon  it.  Sometimes  the  sand 
(quartz)  particles  have  been  fused  or  melted  together, 
so  that  they  hardly  appear  distinct  to  the  eye ;  the  rock 
is  then  known  as  quartz  rock  or  quartzite,  —  a  tough 
substance,  on  which  the  knife-blade  hardly  makes  an 
impression. 

The  granites  we  recognize  easily  through  the  few, 
but  very  distinct,  characters  which  were  indicated  in 
the  last  chapter.  From  them  the  gneisses  differ  in  the 
banded  or  foliated  arrangement  of  the  several  mineral 
elements, — the  quartz,  feldspar,  and  mica,  or  horn- 
blende, —  and  the  various  schists,  by  their  scaly  or 
schistic  structured 

In  the  few  rocks  here  indicated  we  have  probably 
the  materials  of  nine-tenths  of  all  the  known  rocks 
that  go  to  make  up  the  earth's  crust.  There  are  not 
those  hundreds  and  thousands  that  ^some  believe  to 
exist,  nor  is  there  any  real  difficulty  in  finding  out 
what  an  average  rock  is  when  one  quietly  analyzes 
it  by  the  few  tests  that  have  been  given,  —  of  the 
eye,  the  knife-blade,  and  the  acid,  and  with  them 
a  generous  admixture  of  common-sense.  But  the  im- 
portant facts  of  geology  are  not  those  that  tell  us  what 
a  rock  is,  but  what  the  rock  itself  teaches. 


38  THE  EARTH  AND  ITS   STORY. 

Fossil  Imprints  in  the  Rock  ;  Ripples.  — -  In  a  quarry 
of  red  sandstone  and  shale  which  lies  at  a  little  distance 
from  the  road  over  which  my  calling  carries  me,  there  is 
what  quarrymen  and  geologists  call  a  big  "  exposure  " 
of  rock.  The  rock  is  piled  up,  bed  upon  bed,  in  hori- 
zontal or  nearly  horizontal  layers,  perhaps  to  a  height 
of  seventy-five  or  a  hundred  feet.  With  the  good-will 
of  my  workingmen  friends  I  have  sat  for  hours  in  the 
pit  by  the  side  of  the  hoisting  derrick,  eagerly  watching 
the  fresh  faces  of  the  rocks  that  were  being  pulled  out, 
and  hoping  for  something  new.  Time  and  time  again 
had  I  searched  and  searched  in  vain ;  but  to  him  who 
looks  long  enough,  something  is  almost  sure  to  come. 
And  so  it  was  when  one  day  the  rock  split,  and  dis- 
closed on  its  inner  face  beautifully  formed  ripple-marks. 
There  were  the  unmistakable  impressions  of  moving 
water  made  when  the  rock  was  still  soft  —  a  mud. 
Across  the  ripple-marks,  and  completely  obliterating 
some  of  them,  was  a  number  of  distinct  impressions 
of  the  feet  of  some  animal  that  chanced  to  find  its  way 
to  this  mud,  and  across  which  it  manifestly  walked. 
Time  had  effected  wonderful  changes.  The  soft  mud, 
with  its  impressions  and  carvings,  was  now  hard  rock, 
and  what  was  once  the  free  surface  was  now  buried 
about  fifty  feet  by  other  rock  that  had  accumulated 
over  it.  This  being  an  early  discovery  of  my  student- 
ship, I  wondered  long  how  a  surface  of  this  kind  could 
be  buried  by  other  rock.  Then  the  thought  came  to 
me  that,  if  the  ripple-marked  mud  was  the  ancient  bank 
of  a  river,  it  might  easily  have  been  covered,  time  after 
time,  by  the  muddy  floods  of  that  river ;  that  the  rivers 
themselves  often  raise  their  beds  by  heaping  mud  and 


UNIVERSITY 

OF 


Plate  5 


ROCK  IMPRESSIONS. 

1.  Ancient  ripples  in  rock  of  Silurian  age. 

2.  A  block  of  Triassic  shale,  with  sun-cracks  and  footprints  of  a  giant  amphibian 

(salamandroid  ?). 


Plate  6. 


KOCK  IMPRESSIONS. 

A  slab  of  Triassic  shale,  showing  three-toed  and  bird-like  track  of  a  reptile.  The  pits 
scattered  over  the  surface  are  the  impressions  of  raindrops  —  the  evidence 
of  rain  falling  at  this  early  period. 


WHAT  ROCKS  LOOK  LIKE  IN   THE  FIELD.        39 

sand  upon  them,  and  thus  flood  upon  flood  would  build 
up  rock  upon  rock.  Again,  if  the  ripple-marked  rock 
represented  an  ancient  oceanic  shore-mud,  it  might 
have  been  swept  over  by  fresh  oceanic  sands  and  muds 
when  the  water  rose  above  it ;  but  a  great  thickness  of 
covering  could  only  be  made  when,  for  some  reason 
or  other,  the  waters  of  the  sea  rose  very  much  higher 
than  the  usual  high-water  mark,  or  the  land  sunk 
beneath  them.  Both  of  these  conditions,  as  we  shall 
learn  later  on,  took  place  repeatedly  in  the  course  of 
the  earth's  history.  (Plate  5,  Figs.  1  and  2.) 

Footprints  and  Raindrops  in  the  Sands  of  Time.  - 
Years  later,  in  wandering  through  one  of  the  large 
museums  of  our  country,  I  stumbled  upon  a  big  block 
of  the  same  kind  of  stone,  —  the  ripple-marks  were  as 
distinct  as  upon  my  own  specimen,  and  the  footprints, 
if  anything,  still  more  distinct.  But  the  label  attached 
to  the  specimen  stated  that  the  whole  surface  was 
pitted  with  raindrop  impressions,  —  "  fossil  raindrops," 
—  and  there  they  really  were,  the  evidence  forged  in 
the  rock  that  rain  fell  over  a  certain  mud-flat  millions  of 
years  ago !  On  looking  attentively  at  the  rock-surface, 
it  became  manifest  that  the  animal  which  walked  over 
the  rock  had  been  caught  in  this  rain ;  for  many  of  the 
raindrop  impressions  were  in  the  animal's  footprints, 
and  many  others  were  obliterated  by  them.  Here  was 
a  history  of  the  times  complete  in  itself,  and  inscribed 
in  characters  far  more  durable  than  any  that  man  him- 
self has  been  able  to  manufacture.  (Plate  6.) 

What  Rock-Strata  Signify.  —  We  have  now  learned 
from  our  quarry  that  the  different  beds  of  rock  which 
lie  one  on  top  of  the  other  are  the  ancient  muds  or 


40  THE  EAETH  AND  ITS   STORY. 

sands  that  have  been  laid  down  peacefully  by  over- 
flows of  river  or  ocean  waters.  Technically,  these  beds 
are  known  as  strata  (singular  stratum,  which  'means  a 
layer  or  bed),  and  all  rocks  that  show  in  themselves 
this  construction  of  strata  are  called  stratified  rocks. 
As  an  alternative,  they  are  frequently  spoken  of  as 
sedimentary  rocks,  inasmuch  as  they  represent  the  sedi- 
ments of  ancient  waters,  whatever  the  kind  of  water 
may  have  been.  Where  the  strata  occur  in  horizontal 
or  nearly  horizontal  lines,  it  is  a  proof  that  there  has 
been  no  forcible  disturbance  in  the  region  occupied  by 
them,  the  rock-beds  being  very  nearly  or  exactly  in  the 
positions  in  which  the  muds  or  sands  were  originally 
laid  down.  Sediments  in  this  position  are  found  in 
many  parts  of  our  continent  measuring  thousands  of 
feet  in  thickness.  (Plate  7,  Fig.  1.) 

Disturbed  Rock-Masses.  —  Rock-strata  do  not  always 
lie  horizontally.  Sometimes  they  are  gently  arched,  at 
other  times  very  strongly  so.  In  such  cases  there  has 
manifestly  been  some  disturbance  in  the  earth's  crust 
since  the  rocks  were  formed,  as  they  never  could  have 
been  deposited  by  water  in  irregular  positions  of  this 
kind.  Indeed,  we  not  infrequently  find  the  rock,  be  it 
limestone,  shale,  or  sandstone,  standing  with  the  beds 
on  end,  or  vertically,  showing  that  they  had  been 
turned  over  on  themselves  fully  ninety  degrees.  In 
some  cases  the  upturning  has  gone  still  farther,  and 
completely  reversed  the  rock ;  and  finally  there  are  not 
a  few  places  where  the  strata  have  been  so  turned, 
twisted,  and  folded  upon  themselves  that  it  becomes 
a  matter  of  difficulty  to  determine  their  true  relation- 
ships. We  ask  ourselves  the  question :  What  kind  of 


WHAT  BOCKS  LOOK  LIKE  IN   THE  FIELD.        41 

a  disturbance  could  have  brought  this  about?  Almost 
the  only  answer  that  can  be  given  to  this  question  is, 
that  something  caused  the  earth  to  pull  and  push,  and 
that  the  rock  gave  way  under  the  strain  that  was  im- 
posed upon  it.  Probably  in  most  cases  the  movement 
was  brought  about  by  a  general  contraction  of  the 
earth's  mass,  due  to  its  continued  cooling.  When  an 
autumn  apple  shrivels  through  exposure  to  cold,  it 
pulls  itself  together,  and  with  it  goes  the  puckering 
skin.  The  same  thing  must  have  repeatedly  happened 
with  the  "skin"  of  the  earth,  the  rock-crust,  and  hence 
the  endless  puckerings  and  foldings.  (Plates  8-11.) 

Rock-Folding.  —  It  is  at  first  difficult  to  realize  the 
extent  to  which  rocks  have  been  folded.  Often,  when 
we  find  them  lying  in  apparently  horizontal  positions, 
the  horizon  tali  ty  may  only  be  the  expression  of  a  very 
flat  giant  curve  or  arch,  whose  span  covers  perhaps 
miles  of  country.  Also,  when  the  beds  stand  vertically, 
they  are  usually  only  part  of  great  arches  or  sharp  zig- 
zag folds,  whose  tops  have  been  carried  away,  in  the 
course  of  ages,  through  decay,  and  the  destroying  power 
of  water. 

But  we  can  well  turn  from  the  contemplation  of  the 
grand  to  the  study  of  the  insignificant.  If  rocks  have 
been  folded  and  twisted  upon  themselves  on  a  most 
gigantic  scale,  it  is  equally  true  that  often  they  have 
been  folded  so  minutely  as  to  show  all  the  evidences  of 
disturbance  in  hand  specimens.  I  have  a  slab  of  talc 
or  soapstone  which  measures  only  a  few  inches  across, 
and  yet  from  its  many  puckerings  it  resembles  a  piece 
of  corrugated  iron.  In  a  specimen  of  gneiss  the  fold- 
ings can  be  followed1  down  to  the  dimensions  of  a  quar- 


42  THE  EARTH  AND   ITS   STOEY. 

ter  of  an  inch,  or  even  less.  It  is  no  easy  matter  to 
conceive  at  first  sight  how  hard  and  solid  rock  can  be 
folded  in  this  way,  but  that  it  does  so  fold  is  beyond 
question.  More  than  this,  even  the  shells  and  skele- 
tons that  are  enclosed  by  the  rock  as  fossil  remains 
partake  of  the  general  disturbances.  They  are  often 
pulled  out,  twisted,  or  otherwise  deformed,  and  yet 
show  no  signs  of  breakage.  It  seems  to  be  a  fact  that 
any  substance,  no  matter  how  firm  or  rigid  it  may  be, 
no  matter  how  fragile,  can  be  deformed  through  long- 
continued  pressure.  Arctic  travellers  have  frequently 
called  attention  to  the  fact  that  great  flat  cakes  of  ice 
will  in  course  of  time  sag  and  warp  through  their  own 
weight,  curving  under  in  the  most  interesting  manner ; 
and  in  the  possession  of  one  of  our  institutions  of 
learning  is  a  large,  old-fashioned  tombstone,  which  has 
"hollowed"  quite  extensively  through  sagging  between 
the  four  stone  posts  which  held  up  the  corners.  That 
the  movements  in  the  earth's  crust  which  caused  rock 
deformation  were  of  the  slow  and  continuous  kind  is 
borne  out  by  much  evidence. 

The  Positions  Occupied  by  Rocks  ;  Dip.  —  The  knowl- 
edge that  we  have  just  acquired  permits  us  easily  to 
appreciate  the  different  positions  which  rocks  occupy 
in  the  field,  in  the  quarry,  and  in  the  mountain  side. 
The  horizontal,  the  vertical,  the  steeply  inclined,  and 
the  twisted  and  folded  are  merely  the  links  of  a  single 
chain,  and  each  for  itself  represents  a  condition  that 
was  imposed  upon  the  rock-mass.  Quarrymen  and 
geologists  use  a  convenient  word  to  indicate  a  depar- 
ture from  the  horizontal  position ;  they  say  that  the 
rock  "dips."  The  steepness  or  amount  of  dip,  by 


I   UNIVERSITY  ) 
V  / 


Plate  7. 


THE  POSITIONS  OF  ROCK-MASSES. 

1.  Horizontal  strata,  near  Quebec,  Canada. 

».  Outcrop  of  coal  in  the  Pennsylvania  region;  the  strata  appear  on  their  edges  hor- 
izontal; but  the  oblique  arrow  indicates  the  actual  face  of  the  beds,  showing 
that  they  are  steeply  inclined. 


Plate  8. 


THE  POSITIONS   OF  ROCK-MASSES. 
.1.   Steeply  inclined  limestone  strata,  in  Potts's  Quarry,  near  Philadelphia;  the  "  strike ' 

and  "  dip  "  are  both  indicated  by  the  arrows. 
2.    Steeply  inclined  strata  of  limestone  along  the  Schuylkill  River. 


WHAT  ROCKS  LOOK  LIKE  IN   THE  FIELD.       43 

which  we  mean  the  extent  of  departure  from  the  nor- 
mal horizontal  line,  is  measured  by  degrees;  thus  we 
say  the  rocks  dip  45°,  or  30°,  or  25°,  as  the  case  may 
be.  When  the  beds  stand  vertically  they  occupy  the 
position  of  90°  dip.  The  direction  toward  which  the 
rock  drops  or  dips  is  determined  by  the  compass  ;  thus 
we  say,  geographically,  the  rock  dips  to  the  north-west, 
or  to  the  south-west,  etc.,  by  which  we  mean  that  the 
slope  of  the  beds  points  in  those  directions.  (Plate  8.) 


44  THE  EARTH  AND  ITS   STOEY. 


CHAPTER   IV. 

WHAT    A    MOUNTAIN   TEACHES. 

IF  in  your  rambles  through  a  mountain  region  you 
have  a  will  strong  enough  to  turn  the  mind  at  times 
from  the  contemplation  of  the  grandeur  of  scenery  to 
a  study  of  that  which  makes  up  scenery,  you  will 
easily  ascertain  three  facts  as  the  outcome  of  your 
investigations :  1,  that,  with  comparatively  few  excep- 
tions, mountains  always  occur  in  disturbed  areas  of  the 
earth's  crust ;  2,  that,  as  a  necessary  consequence,  their 
rocks  are  badly  tilted,  curved,  folded,  and  broken ;  and 
3,  that  these  twists,  curves,  and  folds  are  merely  an 
amplification  of  the  similar  conditions  which  we  have 
already  learned  to  know  in  the  rocks  of  the  field  and 
in  hand  specimens.  How  often  have  we  looked  with 
wondering  eyes  upon  those  majestic  Alpine  peaks,  tow- 
ering perhaps  two  or  three  miles  into  the  air,  whose 
naked  rocks,  folded  and  zigzagged  upon  themselves, 
plainly  record  the  history  of  the  strife  and  struggle  that 
are  involved  in  the  process  of  mountain-making.  Even 
to-day,  long  after  Nature  has  worked  hard  to  efface 
what  she  has  reared  up,  many  mountains  retain  in  their 
contours  nearly  the  exact  outlines  which  were  given  to 
them. when  the  rocks  were  first  thrown  up  to  aid  in 
their  construction ;  others  are  merely  wrecks  of  former 
greatness,  monuments  to  the  destroying  hand  of  Time. 


WHAT  A  MOUNTAIN   TEACHES.  45 

How  Mountains  may  be  formed.  —  Perhaps  the  sim- 
plest mountain  that  we  can  picture  to  ourselves  as 
having  been  formed  through  a  contraction  of  the  earth's 
mass  is  a  single  fold  of  rock-strata.  If  you  place  on 
the  table  a  number  of  napkins  or  table-cloths,  one  upon 
another,  and  push  gently  from  the  opposite  sides,  you 
are  likely  to  force  up  a  fold  of  this  kind.  Your  push- 
ing is  only  the  equivalent  of  the  pulling  in  of  the 
earth's  crust,  and  the  napkins  may  be  taken  to  be  the 
rock-strata.  If  you  continue  pushing,  you  will  probably 
raise  up  a  number  of  distinct  folds  running  parallel  to 
one  another.  So,  in  the  case  of  the  earth's  crust,  con- 
tinued or  excessive  strain  has  reared  up  parallel  folds  of 
rock,  and  these  are  the  backbones  of  mountain  chains. 

Mountains  of  Simple  Folding ;  Strike,  Anticlines, 
Synclines.  —  Many  a  freshly  born  mountain  chain  had 
this  simple  structure  of  parallel  arched  ridges  and 
separating  longitudinal  troughs  or  "  valleys,"  and  there 
are  some  which  even  to-day  retain  it.  Our  own  Alle- 
ghany  Mountains  had  it  once,  and  so  did  the  Jura 
Mountains  of  France  and  Switzerland.  Were  a  cut  to 
be  made  clean  across  the  trend,  or  strike,  of  such  a 
series  of  mountain  backbones,  it  would  show  the  rocks 
arching  beautifully  upward  to  form  the  mountains,  and 
falling  basin-like  beneath  the  valleys ;  geologists  speak 
of  the  upward  falling  arches  as  anticlines,  and  of  the 
descending  ones  as  synclines.  (Plates  9,  50,  and  51.) 

Had  all  mountain  chains  the  simple  structure  that 
has  here  been  described,  there  would  be  little  difficulty 
in  reading  their  full  history.  Unfortunately,  in  geology, 
complexity,  rather  than  simplicity,  is  the  rule;  and 
many  a  hard  nut  has  to  be  cracked  before  we  can  satis- 


46  THE  EAETII  AND  ITS   STOEY. 

factorily  answer  to  ourselves  what  appears  to  be  the 
simplest  of  questions.  Especially  complex  are  the  con- 
ditions that  are  presented  by  mountain  masses,  and 
frequently  years  of  close  and  continuous  study  are 
needed  to  make  these  conditions  properly  understood. 
It  is  not  necessarily  one  disturbance  alone  which  has 
made  a  mountain  range  or  system ;  but  more  commonly 
a  number  of  distinct  disturbances  have  followed  one 
another  at  irregular,  and  perhaps  far-removed,  periods 
of  time.  The  mountain  has  had,  so  to  say,  several 
"makings,"  and  with  each  of  these  the  rocks  have  been 
further  pushed,  folded,  and  broken;  the  arrangement 
of  the  beds,  or  strata,  may  in  this  way  become  almost 
hopelessly  intricate  and  confusing. 

Overturnings  and  Mountain  Travel  ("  Shearing  ").— 
In  the  work  of  compression  and  crushing,  the  beds 
have  not  infrequently  been  turned  completely  over 
upon  themselves,  so  that  bottom  rocks  have  come  to  be 
located  on  top,  and  the  top  rocks  at  the  bottom.  Some 
notion  of  the  intensity  of  this  earth-strain  may  be  had 
from  the  fact  that  certain  mountain  masses  have  been 
moved  bodily  miles  from  the  positions  which  they  had 
at  one  time  occupied,  and  this  movement  has  in  some 
cases '  been  over  the  tops  of  other  mountains.  Such 
"  shearing  "  movements  were  involved  in  the  making  of 
the  Scottish  Highlands,  in  the  Alps,  etc.  Of  course 
all  this  was  a  slow  process ;  ages  may  have  been  in- 
volved in  the  moving,  as  certainly  they  were  required 
for  the  actual  rearing  of  the  mountains  themselves.  It 
was  not  the  matter  of  a  few  years,  but  probably  of 
hundreds,  or  even  thousands,  of  years. 

Dislocations  ;   Faults.  —  All  over  the  earth's  surface, 


THE  POSITIONS  OF  ROCK-MASSES. 

1.  An  anticlinal  arch  near  Hancock,  Md. 

2.  A  synclinal  fold  in  the  coal  of  the  Hazleton  basin,  Pennsylvania. 


Plate  10. 


THE  POSITIONS  OF  BOCK-MASSES. 

1.  Sharply  folded  strata  of  sandstone. 

2.  Sharply  folded  beds  of  limestone  passing  into  a  "fault,"  or  fracture  with  dis- 

placement. 


WHAT  A   MOUNTAIN  TEACHES.  47 

or  through  the  crust,  there  are  evidences  of  prodigious 
breaks  across  the  rocks,  some  of  these  running  across 
thousands  of  feet  of  rock  thickness  in  an  almost  direct 
course.  At  times  these  rock  fractures  make  no  displace- 
ment in  the  position  of  the  beds  which  they  traverse ; 
at  other  times  they  throw  them  to  one  side  or  another, 
sometimes  elevating  the  strata  on  one  side  of  the  break, 
sometimes  dropping  them.  Breakages  of  this  kind  are 
known  to  the  geologist  as  faults,  because  they  have 
"faulted"  the  rock.  There  is  hardly  a  mountain  mass 
that  does  not  exhibit  within  itself  the  evidence  of 
breakages  and  faults ;  they  are  so  abundant  at  times 
that  the  rock  may  be  said  to  be  completely  parcelled  up 
by  them.  Coal-miners  only  too  well  know  what  a  dis- 
jointed material  —  the  coal  and  adjacent  shale  —  they 
have  to  deal  with  in  their  underground  workings.  Big 
faults  and  little  faults  (these  sometimes  so  small  as 
to  measure  only  a  few  inches)  crowd  in  so  rapidly 
as  to  thwart  the  operation  of  mining  almost  continu- 
ously. There  is  in  my  possession  a  section  of  cobble- 
stone which  shows  it  to  have  been  broken  across  in  not 
less  than  five  places ;  and  yet  the  same  kind  of  force 
which  produced  the  breakages  must  have  helped  at 
another  time  to  unite  the  separate  pieces,  for  the  cob- 
blestone (showing  clearly  the  lines  of  fracture)  is  one 
single  piece  again.  (Plates  10  and  51.) 

Fallen  Blocks  of  the  Crust ;  Continental  Buttresses 
("Horsts").  —  The  further  and  more  carefully  we 
carry  the  eye  through  the  testimony  of  the  rocks,  the 
more  clear  does  it  become  that  at  least  the  superficial 
part  of  our  planet  has  undergone  repeated  breakages, 
and  that  these  are  continuing  well  on  into  our  own 


48  THE  EARTH  AND  ITS   STORY. 

day.  That  which  we  have  habitually  called  the  "  solid 
crust"  is  being  irregularly  dismembered,  or  sectioned 
up  into  elevated  " bosses"  and  fallen  "troughs."  Parts 
of  what  had  at  one  time  been  more  or  less  continu- 
ous land-areas  now  lie  buried  beneath  the  sea,  having 
fallen  bodily  beneath  the  level  of  the  oceanic  waters. 
The  basin  of  the  Mediterranean  is  one  of  these  fallen 
blocks  of  the  earth ;  the  Gulf  of  Mexico  is  probably 
another ;  and  not  unlikely  a  large  part  of  the  Atlantic 
itself  is  a  third,  or,  in  fact,  several  blocks  which  have 
fallen  one  after  the  other.  Between  the  eastern  coast 
of  the  continent  of  Asia  and  the  outlying  volcanic 
islands  —  Kurile,  Japan,  Loo-Choo,  etc.  —  is  a  series 
of  half  land-locked  waters,  the  Japanese,  Yellow,  and 
Kamchatka  Seas,  which  occupy  positions  that  were 
formerly  incorporated  with  the  dry  land.  In  the  same 
way  the  North  Sea  and  the  passageways  leading  from 
it  to  the  open  Atlantic  are  located  on  subsided  or 
broken-through  parts  of  the  older  continent  of  Europe. 
In  the  heart  of  many  of  the  countries  which  to-day 
smile  peacefully  beneath  their  seemingly  quiescent  con- 
ditions breakages  are  still  continuing,  just  as  they  had 
been  going  on  for  ages  in  the  past.  France  and  Ger- 
many and  Italy  all  show  their  broken  parts  —  the  but- 
tresses (or  horsts)  —  that  have  remained  standing  be- 
tween the  breaks  and  the  deep  depressions  which  mark 
the  positions  of  the  breaks  themselves.  The  deep  hol- 
low of  the  Dead  Sea  basin,  the  narrow  basin  of  the  Red 
Sea,  the  trough  of  Lake  Tanganyika  in  EastrCentral 
Africa,  the  Gulf  of  California,  and  even  our  own  pic- 
turesque Yosemite  Valley,  are  seemingly  only  subsided 
parts  or  blocks  of  continents. 


WHAT  A  MOUNTAIN  TEACHES.  49 

Crustal  Breakages  and  Mountain-making.  —  It  is  a 
significant  fact  that  nearly  all  the  great  breakages  of 
the  crust  stand  in  close  relation  with  the  making  of 
mountains.  Thus,  the  successive  falls  of  the  Mediter- 
ranean basin  were  associated  with  the  rearing  up  of  the 
Alps  and  Apennines ;  those  of  the  Mexican  and  Carib- 
bean basins  with  the  mountain  elevations  which  run  in 
disjointed  spots  or  lines  (in  olden  times  continuously) 
through  the  Lesser  and  Greater  Antilles.  Probably  the 
side-pressure  that  was  exerted  by  the  fall  was  mainly 
instrumental  in  "squeezing"  up  the  mountains,  while 
the  break  itself  was  determined  by  a  previously  existing 
weakness  in  the  crust.  It  is  a  long-continued  and  not 
sudden  history  that  is  read  in  those  breakages,  one 
that  is  measured  not  by  years,  but  by  centuries.  And 
yet  we  know  that  even  in  our  own  times,  following  or 
accompanying  earthquakes,  parts  of  the  land-surface 
have  been  lowered,  and  lowered  suddenly,  through  a 
half-score  of  feet  or  more.  Only  so  recently  as  the 
events  of  1893  in  Phocis,  Greece,  have  we  had  proof 
of  this ;  water-channels  were  at  that  time  measurably 
deepened,  and  peninsulas  existing  as  such  for  centuries 
were  broken  up  into  islands.  The  beautiful  islands  of 
modern  and  ancient  Greece  seem  only  to  be  the  sepa- 
rated parts  of  an  old  Greece  which  formerly  extended 
far  into  what  is  now  the  Mediterranean  basin. 


THE    MODELLING    OF    MOUNTAINS    AND    THE    MAKING 
OF    SCENERY;    THE    WORK    OF    WATER. 

It  has  not  happened  to  the  eye  of  existing  man  to 
see  any  large  mountain  newly  formed.     The  mountains 


50  THE  EARTH  AND  ITS   STORY. 

of  to-day  are,  generally  speaking,  ancient;  from  the 
point  of  view  of  the  geologist  some  are  very  ancient, 
others  are  comparatively  modern,  and  many  are  de- 
cidedly new.  Of  the  last-mentioned  we  may  mention 
the  Alps  and  Himalayas ;  of  the  first,  the  Adirondacks 
and  White  Mountains ;  and  among  the  intermediate 
group,  although  removed  from  us  by  certainly  a  few 
millions  of  years,  may  perhaps  be  classed  the  major 
part  of  the  Alleghanies.  But  whether  old  or  new,  all 
have  suffered  changes  that  have  been  brought  to  them 
by  the  hand  of  time,  —  the  result  of  the  work  of  inter- 
nal decay,  and  of  the  ceaseless  destruction  that  comes 
from  the  attack  of  outside  forces. 

How  Water  Works.  —  When  after  a  heavy  rain  you 
wander  out  into  the  freshly  washed  country,  you  cannot 
fail  to  observe  how  muddy  the  numerous  streams  are. 
They  are  carrying  away  the  materials  from  the  solid 
rock,  and  to  that  extent  are  they  helping  to  shape  the 
landscape.  Every  stream,  no  matter  how  insignificant 
it  may  appear,  does  some  work;  and  the  total  of  all 
streams,  when  their  efficiency  is  summed  up,  is  pro- 
digious. But  it  all  goes  back  to  the  tiny  drops  of 
water  that  make  the  streams  —  the  drops  of  rain  or 
the  flakes  of  snow.  In  our  own  gravel-walk  we  see 
what  the  raindrops  do  directly.  They  "  pound  "  out 
the  small  grains  of  sand  that  lie  between  the  pebbles, 
and  loosen  the  whole  for  the  action  of  running  water. 
Under  the  drip  of  your  drain-pipe  the  same  thing  is 
taking  place,  only  perhaps  in  a  more  systematic  way. 
Drop  after  drop  there  falls  into  nearly  the  same  place, 
so  that  a  system  of  earth  modelling  —  a  true  sculpture 
—  is  being  carved  out.  We  see  tiny  pillars  of  sand 


Plate  11. 


THE  POSITIONS  OF  BOCK-MASSES. 

1.  Convoluted  gneiss  of  the  Wissahickon  Valley,  Pa. 

2.  Steeply  pitching   herls  of  hyro-rniea  schist,  at  West  Conshohocken,  Pa.,  showing 

surface  overturn,  or  "  creep." 


2. 
THE  POSITIONS  OF  ROCK-MASSES. 

1.  The  limestone  of  the  Schuylkill  Valley,  Pa.;  the  horizontal  arrow  indicates  the  linti 

of  strike,  the  oblique  one,  the  dip  (30  degrees). 
»,  Folded  gneiss  of  Philadelphia,  with  uncoinformable  clays  (U)  resting  on  top. 


WHAT  A   MOUNTAIN   TEACHES.  51 

and  gravel  standing  in  the  line  of  rain-furrows,  many 
of  them  standing  only  because  they  have  been  protected 
from  down-wash  by  a  hard  capping  of  gravel  —  their 
umbrella,  as  it  were.  How  often,  on  marl  or  sand-heaps, 
have  we  picked  off  pebbles  and  shells  from  the  tops  of 
little  pillars  of  earth  —  pillars  that  stood  out  from  the 
general  mass  because,  under  protection  of  their  own 
hard  covers,  they  for  a  time  successfully  resisted  the 
beating  action  of  rain.  This  may  appear  a  trivial  les- 
son ;  but  it  is  a  key  to  the  understanding  of  that  which, 
developed  on  a  gigantic  scale,  oftentimes  inspires  us 
with  no  less  awe  than  wondrous  admiration. 

Earth  Pillars  and  Monuments.  —  The  great  pillars  of 
earth  which,  in  parts  of  the  Western  United  States,  in 
Wyoming  and  Colorado,  stand  up  by  hundreds  along 
the  mountain  sides  and  in  the  open  valleys,  many  of 
them  capped  by  bowlders  which  are  carried  seventy-five 
or  a  hundred  feet  above  the  general  surface,  are  only 
an  amplification  of  the  tiny  sand-pillars  beneath  the 
pebbles.  They  are  monuments,  and  monuments  on  a 
most  impressive  scale,  of  the  wearing  action  of  water, 
and  are  the  index  that  measures  the  amount  of  destruc- 
tive work  that  has  already  been  accomplished.  To  the 
tops  of  their  highest  points  the  general  surface  of  the 
land  at  one  time  extended,  and  how  much  beyond  can- 
not be  told.  Well  do  they  carry,  in  their  association 
of  ideas,  the  name  of  "  Monument  Parks."  The  fan- 
tastic rocks,  pillars,  and  needles  that  so  picturesquely 
diversify  the  "  Garden  of  the  Gods,"  lying  near  to  the 
foot-hills  of  the  Rocky  Mountains ;  the  castle-like  rock 
buttresses  or  "  birttes  "  which  grimly  look  down  upon 
the  sand- wastes  of  the  western  ''bad-lands;  "  the  "  Pil- 


52  THE  EARTH  AND  ITS  STORY. 

lars  of  Hercules,"  etc.,  that  mark  the  entrances  to  many 
of  the  deep  river  gorges  or  canons,  —  are  only  similar 
witnesses  to  the  destroying  power  of  falling  and  run- 
ning water,  —  the  monuments  that  reconstruct  for  our 
eyes  the  full  landscape  of  which  they  now  constitute 
lingering  remnants.  Before  very  long  they,  too,  will 
have  vanished;  but  for  the  moment  they  teach  us  the 
lesson  of  aqueous  erosion,  the  extent  to  which  the  coun- 
try has  suffered  through  the  eroding  or  wearing  action 
of  water.  Hundreds  of  feet  above  the  great  plains  of 
Wyoming,  over  which  the  railroad  now  courses  to  the 
Pacific,  the  old-time  surface  extended,  as  is  evidenced 
by  the  monuments  which  stare  at  the  traveller  from 
either  side  of  the  road;  but,  unmindful  and  ignorant 
of  the  history  which  these  great  castellated  buttresses 
record,  the  traveller  glances  at  them  merely  from  the 
standpoint  of  curiosity,  or  of  simple  wonderment  at  their 
grotesque  and  imposing  forms.  (Plates  13,  18,  19.) 

Ravines,  Gorges,  Gulches.  —  Just  as  these  huge  tow- 
ers and  pillars  are  the  counterpart  of  the  small  pillars 
that  we  have  seen  fashioned  out  of  the  surface  of  the 
marl-heap  or  in  our  gravel-walk,  so  are  the  deep  ravines 
and  gorges  merely  the  counterparts  of  the  insignificant 
waterways  of  rills  and  rivulets.  What  the  small 
streams  have  done  in  a  small  way,  the  larger  streams 
have  done  in  a  much  larger  way.  They  have  cut  deep 
and  effective  channels,  some  of  which  have  broadened 
out  into  great  open  valleys,  while  others  are  still  re- 
tained so  narrowly  compressed  within  their  boundary 
walls  that  they  present  more  the  aspect  of  earth-rifts 
than  anything  else.  Nearly  all  the  structures  that  AVC 
recognize  under  the  names  of  ravine,  gulch,  defile, 


WHAT  A  MOUNTAIN  TEACHES.  53 

gorge,  clove,  and  canon  are  merely  the  basins  that  have 
been  hollowed  out  by  running  water,  —  the  work  of 
the  carving  tool  that  began  its  operations  when  solid 
rock  first  came  into  existence  with  the  cooling  of  our 
planet,  and  will  continue  them  so  long  as  there  is  water 
on  the  surface  of  the  globe  and  a  sufficiency  of  mois- 
ture in  the  atmosphere. 

The  .Base-Level  of  Erosion ;  Peneplain.  —  The  mind 
can  well  project  itself  into  the  future,  and  see  the  en- 
tire landscape  worn  down  to  a  level  so  nearly  uniform 
as  to  constitute  one  great  flowing  plain.  Any  large 
area  that  has  been  so  washed  down  is  described  as  hav- 
ing been  worn  to  the  base-level  of  erosion,  or  to  that 
point  where  the  main  stream,  as  well  as  its  tributaries, 
is  so  exceedingly  sluggish  as  to  be  no  longer  able  to 
carry  on  the  course  of  destruction.  This  level  is 
reached  when  the  worn-down  surface,  or  peneplain, 
has  fallen  very  nearly  to  the  level  of  the  sea,  below 
which  there  can  be  only  exceptional  erosion.  Let  us 
conceive  that  this  level  has,  in  one  way  or  another,  been 
elevated  high  above  the  sea:  the  waters  of  the  land 
will  then  begin  to  cut  their  courses  anew ;  fresh  vigor 
has  been  given  to  them,  and  once  more  they  work  as 
in  days  of  old.  (Plate  17,  Fig.  2.) 

Canons.  —  There  is  to  be  found  on  the  surface  of 
the  earth  no  more  imposing  lesson  teaching  the  destruc- 
tive work  of  running  water  than  is  furnished  by  the 
deep  river-channels  of   the  Western  United  States,  — 
known   in  the  language  of   the   country  as  caiions,  — 
which  in  sharp  cuts,  usually  of  a  terrace-form,  descend 
thousands  of  feet  through  the  solid  rock,  whether  it 
be    sandstone,    limestone,    or   granite.       For   ages    the 


54  THE  EA11TH  AND  ITS   STOBT. 

waters  have  been  cutting,  and  are  still  cutting  to-day, 
slowly  but  steadily  working  clown  to  that  level  - 
the  level  of  the  sea  —  where  there  is  no  longer  a  fall, 
and  when  of  necessity  this  kind  of  work  must  cease. 
If  the  land  should  progressively  rise  as  the  cutting 
continues,  then  will  the  process  of  destruction  also 
continue,  with  the  end  always  pointing  to  the  day 
when  the  channel  will  have  been  worked  down  to 
the  sea-level.  The  Grand  Canon,  of  the  Colorado, 
which  in  many  respects  is  the  most  imposing  of  all 
structures  of  its  kind,  has  a  length  of  more  than  200 
miles,  with  a  depth,  in  its  deepest  parts,  of  more  than 
7,000  feet.  At  its  top  it  opens  out  to  a  width  of 
from  eight  to  fifteen  miles;  but  at  the  bottom,  where 
the  turbulent  Colorado  River  tumbles  through  its 
bowldery  course,  it  becomes  so  narrow  that  in  many 
places  even  a  foot-passage  on  either  side  of  the  stream 
is  hardly  possible.  The  same  general  characteristics 
that  are  found  in  the  Colorado  Canon  belong  as  well 
to  its  numerous  tributaries,  and  in  some  the  sharpness 
of  the  cut  is  even  more  emphasized.  In  the  canon  of 
the  Virgin  River,  the  rocky  walls  are  really  the  walls 
of  a  cleft  so  narrow  and  so  profound  that  the  rays 
of  the  sun  hardly  penetrate  to  the  bottom.  The  Royal 
Gorge  of  the  Arkansas  is  of  a  similar  nature,  —  a  nar- 
row chasm  cut  through  granite  walls  which  plunge 
clown  precipitously  to  a  depth  of  2,000  and  2,600  feet. 
It  is  in  truth  possible,  and  even  probable,  that  some  of 
the  narrower  canons,  like  the  one  of  the  Arkansas, 
may  have  been  initially  formed  by  a  splitting  open  of 
the  rock-masses  through  which  the  rivers  now  force 
their  way;  but  certainly  the  major  canons  owe  their 
i 


THE  CASON  OF  THE  ARKANSAS.  —  "  BOYAL  GOBGE. 


WHAT  A  MOUNTAIN  TEACHES.  55 

existence    almost    entirely    to    the    work    of    running 
water.     (Plates  13,  14.) 

Old  and  New  Features  in  a  Landscape ;  Valleys.  — 
It  has  been  said  that  ages  were  involved  in  the  cutting 
of  the  caiions,  and  yet  the  geologist  looks  upon  them 
as  young  or  youthful  features  in  the  landscape ;  we 
know  in  a  general  way  the  limit  of  age,  for  they  cannot 
be  older  than  the  top  rock  in  which  they  began  their 
work,  and  this  rock  is  a  comparatively  new  one  in  the 
construction  of  the  earth.  Perhaps  a  hundred  thou- 
sand years,  or  two  hundred  thousand  years,  cover  the 
full  period  of  their  existence.  We  have  canons  in 
other  parts  of  the  world,  —  the  gorge  of  the  Niagara 
River  is  one,  —  but  in  many  we  hardly  recognize  the 
features  that  belong  to  the  western  type.  The  work 
of  time  has  expanded  their  measure,  the  steep  walls 
have  gradually  faded  away  under  the  effects  of  atmos- 
pheric erosion ;  other  streams  have  worked  their  way  in 
and  out ;  and,  finally,  in  place  of  the  narrow  oppressive 
chasm,  we  have  the  genial  and  sunshiny  open  yalley,  — 
the  valley  with  flowing  outlines,  the  plain  that  has  be- 
come suited  to  the  wants  of  man,  and  productive  in  the 
development  of  nature's  resources.  In  such  we  have 
"  old "  features  in  the  landscape ;  for  every  landscape 
may  be  said  to  contain  features  that  mark  periods  of 
youth,  middle  age,  and  maturity.  (Plates  16,  IT,  18.) 

Mountain  Valleys  and  the  Conditions  of  Scenery.  — 
Our  study  of  the  primitive  mountain  chain  has  clearly 
shown  how,  through  a  folding  of  the  earth's  crust,  a 
number  of  parallel  ridges  may  be  formed,  ridges  that 
are  separated  by  a  parallel  series  of  hollows  or  troughs. 
These  hollows  can  justly  be  called  longitudinal  valleys. 


56  THE  EARTH  AND  ITS   STORY. 

since  they  run  longitudinally  with  the  mountain  Lack- 
bones.  But  it  is  not  often  that  one  sees  so  simple  an 
arrangement  of  parts  in  a  mountain  region.  More 
commonly  there  is  a  bewildering  assortment  of  moun- 
tain peaks,  of  disjointed  mountain  buttresses,  of  valleys 
running  in  one  way  and  of  valleys  running  in  another 
way,  some  following  closely  the  trend  of  the  hills,  - 
if  any  trend  is  at  all  discernible,  —  others  cutting  com- 
pletely across  it.  We  are  in  a  true  mountain  wilder- 
ness, where  the  landscape  owes  much  or  most  of  its 
disturbing  irregularities  to  the  wash  of  water.  From 
the  first  moment  that  mountain  began  to  be  mountain, 
the  ceaseless  energies  of  falling  and  running  water 
began  to  destroy  it ;  and  it  will  be  readily  understood 
that  the  destruction  or  levelling  down  of  any  mountain, 
no  matter  how  great,  how  majestic,  or  how  imposing, 
is  merely  a  matter  of  time.  It  is  to  this  destruction, 
to  the  irregular  manner  in  which  the  destruction  is 
carried  through,  that  we  owe  that  diversity  of  form 
which  in  a  landscape  makes  scenery.  Without  it  there 
would  be  no  peaks,  pinnacles,  or  needles,  no  deep 
gorges  or  canons ;  the  cataract  would  be  silent,  and 
the  whole  landscape  would  wear  a  monotonous  garb. 

Transverse  Valleys  ;  Water-Gaps.  —  No  one  who  has 
visited  a  mountain  region  can  have  failed  to  notice  the 
numerous  streams  that  go  tumbling  down  the  mountain 
sides.  Some  are  truly  insignificant,  others  ura  much 
more  important;  but  one  and.  all,  whether  large  or 
small,  are  steadily  eating  their  way  buck  into  the 
mountain  core,  gashing  the  steep  slopes  with  so  many 
distinct  cuts  or  channels.  And  if  the  mountain  is  a 
simple  ridge  or  backbone,  what  is  being  done  on  one 


Plate  15. 


THE  WORK  OF  BIVERS. 

1 .  River-cut  across  the  mountains,  Glenwood  Springs,  Col. 

2.  Gap  of  the  Bow  Kiver,  Alberta. 


Plate  16. 


THE  WORK  OF  RIVERS. 

1.  Plain-making  by  a  river;  the  Delaware  above  the  Water  Gap,  Pa. 

2.  The  course  of  the  Grand  River,  region  of  the  Yellowstone ;  the  rocky  eminence  on 

the  right  is  an  "escarpment."     Both  rivers,  in  conjunction  with  atmospheric 
destruction,  have  formed  broad,  open  plains. 


WHAT  A   MOUNTAIN   TEACHES.  57 

side  is  almost  certainly  being  done  on  the  opposite. 
Some  of  the  streams  work  faster  than  others  ;  they  have 
more  volume  of  water,  a  steeper  slope,  and  perhaps 
more  crumbling  rock  to  work  through;  while  the  less 
powerful  ones  have  only  succeeded  in  carving  from  the 
mountain  side  troughs  or  valleys  of  moderate  extent, 
these  may  have  gained  to  the  very  heart  of  the  bar- 
rier, and  perhaps  cut  it  completely  through  and  down. 
Then  we  should  have  a  transverse  (cut  or)  valley  formed, 
and  unquestionably  many  of  the  structures  of  to-day 
which  hold  this  relation  have  been  formed  in  this  man- 
ner. Who  can  look  deeply  into  the  gorges  and  "  cloves" 
of  the  beautiful  Catskill  region  without  recognizing  this 
condition !  Some  of  them  hang  high  up  on  the  moun- 
tain slopes ;  others  have  been  cut  completely  through, 
and  take  the  drainage  from  the  two  sides  of  the  moun- 
tain. The  mountain  has  been  "gapped."  (Plate  15.) 

The  very  much  frequented  summer  locality  in  the 
State  of  Pennsylvania  known  as  the  Water  Gap  de- 
rives its  name  from  the  circumstance  that  the  Delaware 
River  at  that  point  cuts  its  way  transversely  through 
the  hard  rock  of  the  Kittatinny  or  Blue  Mountains. 
When  I  first  visited  the  locality  I  was  impressed  only 
with  the  beauty  of  its  natural  scenery,  the  rugged 
forest-covered  cliffs,  the  placid  river,  and  the  smiling 
fields  lying  on  .either  side  of  the  gap.  Later  I  won- 
dered why  the  Delaware,  which  flowed  so  peacefully 
down  the  valley  on  the  off-side  of  the  gap,  should  have 
suddenly  turned,  and  cut  a  channel  through  the  moun- 
tains, instead  of  simply  following  their  trend.  This 
was  a  puzzle,  and  the  like  of  it  still  puzzles  geographers. 

The  Origin  of  Gaps.  —  The  Water  Gap  is  one  of  a 


58  THE  EARTH  AND   ITS   STORY. 

numerous  series  of  similar  structures  that  are  to  be 
found  in  the  mountains  of  the  Eastern  United  States, 
and  through  which  many  of  the  larger  rivers  break 
their  way  to  the  sea.  The  Hudson  River,  for  example, 
gaps  the  Highlands  of  the  State  of  New  York  at  West 
Point;  the  Lehigh  gaps  the  Blue  Mountains  at  the  Le- 
high  Gap ;  the  Susquehanna  at  several  points  the  Alle- 
ghanies ;  while  the  Potomac  breaks  through  the  Blue 
Ridge  at  Harper's  Ferry.  These  rivers  have  all  taken 
to  breaking  their  courses  at  one  or  more  points  where 
they  approach  the  mountains,  arid  they  largely  repeat 
the  problem  which  is  presented  by  the  Delaware.  We 
are  probably  not  yet  in  a  position  fully  to  understand 
this  action.  In  some  cases,  possibly,  the  trenched  moun- 
tains were  reared  up  by  slow  degrees  in  the  path  of  the 
already  existing  rivers,  which  simply  cut  down  as  fast 
as  elevation  went  up  in  front  of  them ;  in  others  the 
gaps  may  have  been  originally  cut  by  streams  other 
than  those  which  now  occupy  them,  —  a  preparation  for 
occupancy,  as  it  were ;  and  in  most  instances,  perhaps, 
the  explanation  is  to  be  found  in  the  simple  fact  that 
the  contours  of  the  country  are  not  to-day  what  they 
were  formerly,  that  the  positions  of  present  deep  valleys 
are  the  positions  that  for  ages  were  occupied  by  high 
plateaus  and  mountain  masses,  and  that  the  channels 
were  cut  when  the  relations  of  mountain  and  valley 
were  in  a  measure  reversed.  The  Delaware,  as  we 
know  from  positive  facts,  at  one  time  flowed  on  a  high 
level,  —  a  level  above  that  of  the  mountain-top  which 
is  now  cut  through  ;  and  it  was  then,  probabh',  that 
the  cutting  first  began.  In  course  of  time  open  valleys 
have  been  carved  out  on  either  side  of  the  mountain 


Plate  17. 


DENUDATION  OF  THE  LAND-SURFACE. 

1.  A  V-shaped  valley  in  the  Alps. 

2.  The  Vale  of  Cashmere,  an  open  plain  of  long-continued  erosion ;  an  upland  peneplain. 


60  THE  EARTH  AND  ITS   STORY. 

river  terraces,  the  lowest  is  always  the  one  of  newest 
date.     (Plate  18.) 

LAKE-BASINS    AND    MEADOW-LANDS. 

To  most  persons  a  lake-basin  is  merely  a  great  hol- 
low, or  trough,  which  has  been  worked  out  by  the  main 
stream  that  falls  into  it.  Had  the  person  holding  such 
a  notion  put  himself  at  the  position  where  the  said 
stream  or  river  discharges  into  the  lake,  and  carefully 
observed  what  was  going  on  about  him,  he  would  in 
quick  time  have  come  to  an  altogether  different  conclu- 
sion. He  would  have  noted  that  very  little  excavating 
was  being  done  Iby  the  river;  on  the  contrary,  its  only 
visible  work  was  the  filling  in  of  the  lake  with  the  mud 
that  it  was  carrying  to  it.  Far  into  the  basin  is  the 
mud  being  carried ;  and  it  stands  to  reason  that  in  a 
certain  time  the  entire  hollow  will  be  filled  in,  and  the 
lake  made  dry.  Nor  is  this  an  exceptional  lake  occur- 
rence ;  it  is  the  history  of  almost  every  similar  structure 
that  is  to  be  found  on  the  earth's  surface. 

The  Silting  of  Rivers.  —  Rivers  fill  up  the  moment 
their  velocities  have  been  so  reduced  that  they  no 
longer  are  able  to  transport  the  materials  that,  as 
swiftly  flowing  bodies,  they  carry  with  them.  Whether 
it  be  at  the  mouth  of  the  river  at  sea-level,  or  in  the 
more  quiet  lake  basin,  the  same  thing  takes  place ; 
the  river  drops  its'  sediment.  Any  one  who  has  had 
the  good  fortune  to  stand  at  both  ends  of  the  lovely 
lake  of  Geneva,  where  the  muddy  Rhone  enters  on  one 
side  and  leaves  it,  clear  as  crystal,  on  the  opposite,  will 
have  immediately  recognized  the  special  "  straining r' 
quality  of  the  lake ;  it  relieves  the  river  of  its  sedi- 


DENUDATION  OF  THE  LAND-SURFACE. 

The  Giant's  Club,  near  the  Green  River,  Wyoming  — a  remnant  of  the  old  land-surface, 
The  stratification  and  alternation  of  the  beds  are  clearly  denned. 


Plate  20. 


^j 


RECONSTRUCTION  OF  THE  LAND-SURFACE. 

1.   The  terraces,  or  former  water-lines,  of  "Lake  Bonneville,"  the  ancient  (now  dry) 

basin  of  which  the  Great  Salt  Lake  is  a  lingering  fragment. 
'2.    The  valley  of  Engelberg,  Switzerland,  an  old  lake-basin  laid  dry. 


WHAT  A  MOUNTAIN  TEACHES.  61 

merit,  and  by  so  doing  fills  itself  up.  All  over  the  floor 
of  this  lake,  as  well  as  of  all  the  other  large  lakes  of 
Switzerland  (or  of  the  world),  there  is  deposited  a  fine 
river-mud ;  and  one  need  go  but  a  short  distance  beyond 
the  present  confines  of  the  water,  to  discover  that  some 
of  the  adjacent  "  land  "  country  is  merely  a  part  of  the 
ancient  lake-bottom  filled  up  and  laid  dry. 

Meadow-Lands.  —  It  is  in  this  way  that  many  of  our 
most  beautiful  meadows  and  pasture-lands  have  been 
made  to  occupy  the  positions  of  formerly  existing  lakes ; 
they  are,  indeed,  those  lakes  filled  in,  and  sometimes 
still  carry  with  them  the  meandering  stream  which  at 
one  time  was  tributary  to  the  lake.  A  wonderful 
change,  one  is  prompted  to  exclaim ;  but  it  is  one  that 
had  to  come  in  the  course  of  events.  How  pleasantly 
do  we  recall  the  scenery  of  those  beautiful  twin  lakes 
of  Switzerland,  Thun  and  Brienz,  and  how  frequently 
is  the  comparison  made  between  the  scenery  of  the  one 
and  the  scenery  of  the  other ;  but  how  rarely  is  it  rec- 
ognized that  these  two  lakes  were  formerly  one,  and 
that  the  separation  took  place  as  the  result  of  filling 
in.  Few  of  the  many  who  wander  through  the  streets 
of  charming  Interlaken  ponder  the  fact  that  they  are 
walking  over  a  part  of  the  old  lake  of  Thun-Brienz. 
(Plate  20,  Fig.  2.) 

Origin  of  Lake  Basins ;  Crater  Lakes ;  Glacial  Lakes. 
If,  then,  lake  basins  are  not  cut  out  by  moving  water, 
but,  on  the  contrary,  are  filled  up  by  them,  the  inquiry 
naturally  presents  itself :  How  are  such  basins  formed  ? 
Regretfully  it  must  be  said,  there  is  as  yet  no  defi- 
nite answer  to  this  question.  Some  lakes  undoubtedly 
occupy  natural  hollows  in  the  rock;  others,  similar 


62  THE  EARTH  AND  ITS  STOEY. 

hollows  in  deposits  of  gravel,  sand,  or  mud;  and 
many  others,  again,  troughs  that  may  have  been  made 
such  through  rock  movements  and  dislocations.  There 
are  also  lakes,  like  the  lakes  of  Central  and  Southern 
Italy,  and  Crater  Lake  in  Oregon,  which  occupy  the 
crater  hollows  of  formerly  active  volcanoes  ;  and  there 
are  bodies  of  water  which  were  formerly  parts  of  the 
free  ocean,  but  are  now  lakes  through  land-locking  in 
one  form  or  another.  Such  are  the  Lakes  Como  and 
Maggiore  of  North  Italy,  the  Caspian  and  Aral  of 
Eurasia.  In  these  we  still  find  evidences  among  the 
living  animals  of  the  ancient  marine  fauna.  While 
the  lakes  of  the  classes  here  designated  explain  their 
own  origins,  it  is  doubtful  if  the  greater  number  of 
the  lakes,  especially  of  the  Northern  Hemisphere,  can 
be  referred  to  such  simple  types  of  structure.  Their 
occurrence  is  so  markedly  bound  in  with  the  evidences, 
in  the  regions  which  they  occupy,  of  ice-movements, 
that  by  many  geologists  their  basins  are  unhesitatingly 
ascribed  to  the  scouring  and  gouging  action  of  glaciers. 
And  there  is  much  to,  support  this  view.  In  the 
greater  number  of  the  regions  where  glaciers  are  to- 
day largely  developed,  we  find  an  abundance  of  lakes ; 
in  nearly  all  regions  where  glaciers  formerly  existed, 
we  also  find  lakes  and  hollowed  rock-basins ;  and 
where  there  is  no  evidence  of  present  or  past  glacia- 
tion  we  find  but  few  and  insignificant  lakes,  or  only 
those  whose  basins  can  readily  be  explained  on  the 
assumption  of  rock  dislocations.  We  shall  learn  more 
of  this  when  studying  glaciers. 

Ancient  Lake  Basins  ;  Lake  Terraces.  —  Not  far  from 
the  "City  of  the  Saints,"  and  high  up  on  the  slopes 


WHAT  A  MOUNTAIN  TEACHES.  68 

of  the  rugged  mountains  which  descend  to  the  shores 
of  the  Great  Salt  Lake,  the  eye  sees  long  lines  of 
seeming  roadways  winding  around  and  about  the  rocky 
buttresses,  sometimes  in  tiers  of  three,  four,  or  five 
above  one  another.  They  run  in  almost  absolutely 
horizontal  courses,  and  look  precisely  like  artificial 
constructions.  When  we  mount  to  them  we  find  that 
they  are  level  planes,  perhaps  fifty,  or  a  hundred,  or 
even  two  hundred  feet  in  width,  which  project  like 
so  many  terraces  from  the  face  of  the  mountain.  With 
the  lesson  of  the  river  terraces  in  our  mind,  it  is  not 
difficult  to  recognize  that  these  largely  similar  struc- 
tures are  exactly  their  counterpart,  and  represent  the 
old  levels  which  were  formerly  reached  by  the  waters 
of  the  lake.  Fully  a  thousand  feet  higher  than  to-day 
the  waters  of  the  lake,  of  which  the  Great  Salt  Lake 
is  only  a  lingering  fragment,  sometime  extended  ;  at 
that  time,  and  not  very  long  ago  geologically,  the 
waters  were  still  fresh,  and  they  had  a  flowing  outlet 
to  the  north-west.  With  its  great  depth  this  ancient 
lake  —  known  to  geologists  as  Lake  Bonneville  —  cov- 
ered an  enormous  area,  perhaps  ten  times  that  which 
is  covered  by  the  modern  shallow  sea  which  remains 
in  place  of  it.  The  saltiness  came  with  the  gradual 
desiccation  or  "drying  out"  of  the  waters,  a  condition 
which  followed  a  gradual  drying  of  the  American  cli- 
mate itself,  through  what  cause  no  one  yet  positively 
knows.  The  modern  Great  Salt  Lake  has  no  outlet, 
and  the  streams  that  flow  into  it  are  very  nearly  pure 
or  fresh.  Yet  what  little  of  salty  material  they  carry 
in  is  all  locked  up  to  keep,  and  in  this  way  it  ac- 
cumulates year  by  year,  It  is  estimated  that  fully 


64  THE  EARTH  AND  ITS   STORY. 

twenty  thousand  years  were  required  to  give  to  the 
lake  the  saltiness  which  it  now  has  —  a  sixth  by  weight 
of  the  actual  water  itself.  (Plate  20,  Fig.  1.) 

The  Scenery  of  Lake-Shores.  —  So  recent  in  time  has 
been  the  existence  of  the  old  lake,  that  the  shore-cliffs 
and  caves  which  its  ruffled  waters  carved  are  pre- 
served with  a  freshness  which  seemingly  speaks  only 
of  yesterday.  Almost  every  detail  of  water-wear  can 
be  recognized  in  them,  the  same  that  one  sees  to-day 
in  the  cliffs  of  such  a  lake  as  Superior,  or  even  along 
the  ocean  front.  The  practised  eye  can  at  a  glance 
recognize  the  tool  that  has  been  at  work.  There  are 
no  pinnacles,  or  peaks,  or  flowing  outlines  which  dis- 
tinguish the  wear  of  the  atmospheric  waters ;  there 
could  not  be,  as  this  portion  until  recently  was  buried 
within  the  lake- waters,  and  by  them  protected  from 
outside  wear.  Above  the  line  of  the  top  terrace,  how- 
ever, or  beyond  where  the  lake-waters  extended  their 
protecting  influence,  the  scenery  at  once  changes ;  there 
are  no  longer  steeply  pitching  cliffs,  but  in  their  place 
the  usual  rugged  furrows,  flying  buttresses,  and  peaky 
ridges  which  distinguish  the  sculpture  of  the  open 
land-surface. 

The  history  that  is  taught  to  us  by  Lake  Bonneville 
is  repeated  elsewhere  in  the  United  States,  and  in  other 
parts  of  the  earth's  surface.  From  Oregon  southward 
into  what  is  now  the  Great  Basin,  —  a  region  of  in- 
terior drainage,  —  and  over  the  area  now  occupied  in 
part  by  Pyramid,  Humboldt,  Walker,  and  Carson  Lakes, 
stretched  in  former  days  Lake  Lahontan;  and  bodies 
of  water  of  large  extent  at  one  time  covered  perhaps 
the  greater  portion  of  the  present  Mexican  plateau. 


SNOW  AND   GLACIERS.  65 


CHAPTER   V. 

SNOW    AND    GLACIERS. 

THE  traveller  who  in  Switzerland  casts  his  eye  over 
the  wonderful  series  of  mountain  heights  which  there 
diversify  the  landscape,  and  give  to  it  a  grandeur 
which  is  perhaps  to  be  matched  noAvhere  else  on  the 
surface  of  the  earth,  sees  the  upper  portions  of  those 
mountains  bathed  in  snow,  both  during  the  summer 
and  the  winter.  In  the  winter-time  the  snow  crawls 
down  nearer  to  the  valleys  which  echo  with  the  bells  of 
the  pasturing  cattle,  and  hangs  heavily  on  the  branches 
of  the  dark  forest  which  for  a  distance  of  several  thou- 
sand feet  climbs  up  the  rugged  mountain  slopes.  It 
is  there  augmented  by  every  new  snow-fall,  and  dimin- 
ishes as  the  warmth  of  the  sun's  rays  melts  off  the 
material  that  is  furnished  to  it.  In  the  heart  of  the 
summer,  except  in  dark  and  forbidding  gorges  or  rock- 
crevices,  we  rarely  see  snow  below  8,500  or  9,000  feet, 
because  up  to  this  line  the  sun  has  proved  itself  victor 
in  the  contest  for  occupancy;  the  snow  has  steadily 
melted  in  the  path  of  its  coming,  and  by  July  or 
August  has  pretty  generally  disappeared.  Only  above 
8,500  to  9,000  feet  does  it  still  hang  on ;  thinned  off, 
it  yet  resists  the  invasion  of  the  sun,  and  by  its  quan- 
tity manages  to  hold  possession  until  refreshed  by  the 
next  winter's  supply. 


66  THE  EARTH  AND  ITS   STORY. 

Snow-Line.  —  -  The  line  or  level  on  any  mountain 
elevation  beyond  which  more  snow  accumulates  in 
winter  than  the  warmth  of  summer  is  able  to  com- 
pletely remove,  is  known  as  the  line  of  perpetual  snow, 
or  simply  "  snow-line."  We  find  such  a  line  on  almost 
every  extensive  mountain  chain,  and  it  is  present  also 
on  many  isolated  mountain  peaks.  Naturally,  in  re- 
gions like  the  tropics,  where  the  summer  heat  is  great- 
est and  the  winter  cold  least,  this  line  will  occupy  a 
high  position  ;  in  and  toward  the  polar  regions,  on  the 
other  hand,  where  the  conditions  are  reversed,  the  line 
lies  low.  Hence  it  is,  that  while  in  the  Alps  the  line 
of  perpetual  snow  is  found  at  about  8,500  feet,  in  the 
Equatorial  Andes  it  ascends  to  15,000—17,000  feet,  and 
on  the  coast  of  Greenland  descends  to  2,000-3,000  feet. 
On  Mount  Etna,  in  latitude  37°  30'  N.,  it  is  found  at 
about  9,500  feet.  Nowhere,  seemingly,  does  it  descend 
to  the  actual  sea-level.  The  quantity  of  precipitation, 
which  really  measures  the  amount  of  snow  that  can 
accumulate,  has  much  to  do  with  regulating  this  posi- 
tion. On  the  Sierra  Nevada  Mountains  of  California, 
which  by  reason  of  their  nearness  to  the  ocean  receive 
much  moisture  and  a  heavy  snowfall,  the  snow-line  is 
found  at  11,000  feet;  on  the  eastern  Rocky  Moun- 
tains, on  the  other  hand,  to  which  comparatively  lit- 
tle moisture  is  permitted,  owing  to  the  draining  of 
the  clouds  on  the  west,  the  snow-line  rises  to  14,000 
feet. 

The  Mountain  Snows  and  what  becomes  of  them.  - 
Probably  the  question  has  often  presented  itself  to  the 
traveller  :    What  is  the  thickness  of  the  snow-covering 
on   mountains  ?     And   again,    Does  not   this   thickness 


Plate  25. 


THE  ASPECT  OF  A  GLACIER. 


The  upper  portion  of  the  Rhone  Glacier,  Switzerland,  showing  the  crevasses,  the  vertical 
banding  of  the  ice,  and  the   Gletscherkorn,  or  granular  ice   (lower  right-hand 


SNOW  AND   GLACIERS.  67 

increase  from  year  to  year,  or  is  it  nearly  constant 
during  its  existence  ?  It  has  been  ascertained  that  on 
many  of  the  Alpine  summits,  —  the  Jungfrau  and  Piz 
Bernina,  for  example,  —  there  is  generally  a  thickness  of 
snow  from  200  to  300  feet ;  and  not  unlikely  many  of 
the  Himalayan  summits  have  a  still  heavier  covering. 
No  section  of  a  snow-deposit  has  ever  been  measured 
which  much  exceeds  this  development;  yet  there  can 
be  little  doubt  that  in  many  parts  of  the  Arctic  and 
Antarctic  regions  the  quantity  exceeds  this  by  ten  or 
twenty  times.  On  the  other  hand,  it  is  certain  that 
there  are  years  when  this  thickness  is  very  materially 
reduced,  to  the  extent,  indeed,  of  nearly  uncovering  the 
entire  mountains. 

At  first  sight  it  would  appear  that  the  steadily  ac- 
cumulating snow  on  a  mountain  summit,  which  annu- 
ally considerably  exceeds  that  which  is  melted  off  by 
the  summer  heat,  must  in  course  of  time  materially 
augment  the  height  of  that  mountain ;  but  we  know 
from  a  comparison  of  past  and  recent  measurements 
that  this  is  not  the  case.  The  mountain  summits  re- 
main approximately  of  the  same  elevation,  except  in  so 
far  as  they  lose  height  through  their  own  steady  dis- 
integration and  decay.  The  process  that  removes  this 
excess  of  accumulation  is  that  which  is  involved  in  the 
making  of  glaciers. 

What  a  Glacier  is. --The  simplest  definition  of  a 
glacier  is  :  a  more  or  less  united  body  of  ice  which  has 
been  formed  of  the  upper  snows  of  mountains,  and 
with  a  steady,  usually  very  slow,  movement,  slides 
down  the  mountain  side.  By  far  the  greater  number 
of  the  glaciers  of  the  world,  so  far  as  they  are  known 


68  THE  EAETH  AND  ITS  STOEY. 

to  us,  fall  under  this  comprehensive  definition.  In 
rarer  instances,  the  snows  which  make  glaciers  may  of 
themselves  accumulate  and  become  of  sufficient  thicl^- 
ness  without  requiring  the  aid  of  mountain  elevations; 
such  a  condition  we  seem  to  find  both  in  the  Arctic 
and  the  Antarctic  regions. 

For  our  more  intimate  conception  of  this  moving 
river  of  ice  we  turn  to  a  study  of  that  wonderland  of 
glaciers,  Switzerland.  In  old  and  new  books,  with  old 
and  new  travellers,  there  is  one  particular  glacier  of 
the  Alps  to  which,  for  one  cause  or  another,  more 
attention  has  been  given  than  to  any  other.  It  is 
known  as  the  Mer  de  Glace,  one  of  several  ice-streams 
which  descend  from  the  northern  face  of  the  Mont 
Blanc,  and  press  their  streams  as  tributaries  to  the 
mighty  Rhone.  It  does  not  essentially  differ  from  any 
of  the  hundreds  of  other  glaciers  which  exist  near  by, 
nor  is  it  as  massive  as  many  others,  ranking  only  fourth 
in  size  of  all  the  glaciers  of  Switzerland;  but  it  is  in 
a  region  which  is  annually  visited  by  thousands  of  tour- 
ists, and  this  fact  has,  doubtless,  helped  to  make  it  of 
special  interest.  From  a  distance  this  Mer  de  Glace 
presents  the  appearance  of  a  tortuous  snow-filled  valley, 
gently  pitched  in  some  places,  elsewhere  breaking  down 
in  rapid  plunges.  The  white  or  gray  ice,  which  the 
eye  clearly  follows  until  it  loses  itself  in  the  ice-cap, 
seems  like  a  united  body;  but,  as  we  approach  nearer, 
we  find  it  broken  and  torn  in  pieces  by  innumerable 
clefts  and  fissures  (crevasses),  which  traverse  it  in 
various  directions.  What  was  seemingly  a  smooth  sur- 
face is,  on  nearer  acquaintance,  a  mass  of  hundreds  of 
pinnacles  (seracs),  so  wildly  thrown  about  as  to  make 


SNOW  AND   GLACIERS.  69 

travelling  over  and  between  them  a  matter  no  less  diffi- 
cult than  dangerous.  Having  reached  an  elevation  of 
about  3,600  feet,  we  finally  stand  by  the  side  of  the  ice 
itself,  and  for  the  first  time  are  in  a  position  properly 
to  appreciate  the  giant  measure  of  the  object  that  is 
before  us.  Across  a  width  of  considerably  over  2,000 
feet,  the  ice-mass  spreads  out  on  either  side  of  us, 
rising  like  a  steep-sloping  mound  or  hillock,  and  pass- 
ing upwards  for  nearly  six  miles  before  it  is  lost  in  the 
perpetual  snows  of  the  mountain-top.  (Plate  27.) 

The  Moraine;  Glacial  Striae;  Erratics In  front  of 

the  ice,  and  with  the  ice-nose  buried  deep  within  it,  is 
a  vast  rubble  heap  of  bowlders,  pebbles,  angular  rock- 
fragments,  and  sand  materials  which  have  been  brought 
along  in  the  course  of  the  moving  ice,  some  of  them 
by  actual  hard  pushing  for  perhaps  miles,  others  carried 
on  the  free  surface  of  the  ice,  and  by  it  dumped  over 
at  its  termination.  Locally  such  a  heap  has  long  been 
known  as  moraine,  a  name  which  geologists  have  seen 
fit  to  receive  into  their  own  technical  phraseology. 
Where  we  stand,  this  moraine  may  be  thirty-five  or 
fifty  feet  in  height,  elsewhere  rising  considerably  higher, 
and  in  other  places  washed  down  very  nearly  to  the 
level  of  the  glacial  stream,  which  cuts  through  it  and 
issues  from  the  under  surface  of  the  ice  as  a  part  of 
its  melting  waters.  We  examine  many  of  the  bowlders 
and  rock-fragments  that  lie  about  us,  and  note  that 
they  differ  materially  among  themselves.  Some  are 
rounded,  others  are  angular ;  the  first  are  worn  smooth, 
the  latter  are  rough,  not  differing  from  rock-masses  as 
they  present  themselves  on  the  untouched  mountain 
face.  It  takes  little  study  to  convince  us  that  the 


70  THE  EAETH  AND   ITS    STORY. 

round  and  smooth  pebbles  or  bowlders  have  been  worn 
into  their  present  shapes  by  hard  pressure  and  rubbing 
—  the  glacial  ice  has  passed  over  them  or  rubbed  them 
hard  against  their  fellows  ;  we  find  further  evidence  of 
this  in  the  grooves  and  scratches  (atrice)  which  farrow 
their  surfaces,  and  which  record  their  own  history. 
The  angular  blocks  have  manifestly  not  been  so 
troubled,  and  their  travelling  has  been  an  easy  one. 
To  all  these  bowlders,  as  individual  objects,  whether 
large  or  small,  geologists  have  given  the  name  of 
erratics  (wanderers) ;  they  have  travelled  with  the 
glacier,  and  so  far  as  the  ice  goes  and  the  rock-frag- 
ments hold  out  they  go  too.  (Plate  28,  Fig.  1.) 

Terminal  and  Lateral  Moraines.  —  We  follow  round 
this  end  or  terminal  moraine  to  the  sides  of  the  ice- 
stream,  and  find  that  there  are  similar  continuous  heaps 
or  lines  of  rubble  which  run  lengthwise  with  the  glacier, 
or  on  its  right-hand  and  left-hand  sides.  Geologists  are 
in  the  habit  of  designating  these  side  lines  lateral  mo- 
raines, their  position  easily  distinguishing  them  from 
the  end  or  terminal  moraine ;  they  extend  continuously 
for  nearly  the  full  length  of  the  glacier,  generally 
moved  a  little  way  from  the  absolute  margin,  but  fre- 
quently so  far  spilling  over  as  completely  to  obliterate 
the  actual  border  of  the  ice.  The  materials  of  these 
lateral  moraines  have  been  derived  from  the  down- 
falling  debris  of  the  mountain  side,  —  most  of  it,  prob- 
ably, a  result  of  natural  rock-decay,  the  rest  gouged  out 
by  force-pressure  of  the  moving  ice.  (Plates  27,  28.) 

We  have  mounted  on  the  top  of  the  ice.  We  ap- 
proach cautiously  one  of  the  numerous  wicked  crevasses, 
and  look  down  its  narrow  and  gloomy  space.  For  50 


Plate  28. 


i. 


2. 

GLACIAL,  PHENOMENA. 

1.  A  rock-slab  smoothed  and  grooved  (striated)  through  glacial  attrition. 

2.  The  front  wall  of  a  Greenland  glacier,  showing  the  edge  of  the  ice,  its  stratification, 

and  the  end  or  terminal  moraine  in  front. 


SNOW  AND   GLACIEBS.  71 

or  100  feet,  not  rarely  for  200  or  300  feet,  and  occa- 
sionally for  even  greater  depths,  the  eye  can  follow  the 
nearly  vertical  and  adamantine  walls  of  ice,  so  smooth 
in  places  as  to  reflect  the  light  with  the  brilliancy  of  a 
mirror;  elsewhere  long  icy  pendants  or  icicles,  much 
like  the  stalactites  of  limestone  caverns,  hang  closely 
over  the  ice-front,  descending  to  depths  virtually  un- 
known. The  ear  possibly  catches  the  sound  of  running 
water,  for  under-ice  streams  are  plentiful ;  the  waters 
from  the  pelting  ice  all  gain  the  bottom,  and  there 
they  course  about  until  they  unite  in  one  or  more  main 
streams.  In  the  heated  hours  of  the  day  the  surface, 
where  not  molested  by  ragged  crevasses,  is  musical 
with  the  song  of  gurgling  rills  and  rivulets,  which  here 
and  there  cascade  into  the  vertical  clefts,  or  plunge 
into  great  holes  (moulins)  which  they  themselves  have 
in  part  excavated.  In  the  hours  of  night  the  music 
of  the  glacier  usually  ceases,  for  then  the  melting 
has  stopped,  and  there  is  but  little  flow  of  water.  A 
rock  perchance  tumbles  off  its  purchase,  or  the  ice 
creaks  and  groans  under  the  straining  pressure  to 
which  it  is  subjected ;  but  the  ice-river  is  on  the 
whole  silent,  to  be  again  awakened  into  active  life 
with  the  return  of  the  day's  heat.  Its  motion  has  not 
stopped,  however,  although  it  has  slackened ;  winter 
and  summer,  night  and  day,  the  mighty  stream  con- 
tinues pressing  forward,  but  its  movement  is  less  rapid 
in  the  hours  and  periods  of  cold  than  in  those  of  heat. 
As  we  laboriously  climb  over  the  surface  of  the  ice, 
we  note  that  where  the  glacier  is  more  nearly  horizon- 
tal in  position,  or  occupies  a  flat  bed,  the  ice  shows  a 
tendency  toward  unity ;  the  crevasses  have  largely  dis- 


72  THE  EARTH  AND   ITS   STORY. 

appeared,  or  at  least  have  been  so  closed  over  as  hardly 
to  be  visible.  On  the  other  hand,  where  the  glacier 
breaks  from  a  nearly  horizontal  bed  to  one  that  is 
steeply  pitched,  the  surface  becomes  raggedly  crevassed 
and  fractured.  We  conclude,  therefore,  that  the  ice 
has  been  torn  apart  by  travelling  over  an  uneven  and 
irregular  surface,  just  as  would  also  be  the  case  if  the 
travelling  medium  were,  in  place  of  ice,  a  somewhat 
liquefied  mass  of  tar  or  treacle.  On  the  level  parts  of 
the  course  the  rents  or  tears  have  again  been  united  by 
being  pressed  together,  and  the  glacier  presents  a  more 
or  less  solid  body.  Where  it  passes  around  great 
curves  the  ice  also  breaks  and  fractures,  once  more  to 
be  built  together  where  the  stream  regains  its  straight 
course. 

The  Forming  Basin  of  the  Ice  (Neve  or  Firn) .  —  We 
have  now  travelled  five  or  six  miles  over  the  torn  ice- 
sheet,  have  seen  it  where  its  slope  is  so  nearly  flat  that 
its  departure  from  the  horizontal  line  can  hardly  be 
detected  by  the  eye,  and  have  climbed  its  face  where  it 
plunges  cataract-like  at  an  angle  of  fifteen  to  twenty 
degrees.  The  lower  glassy  ice  has  been  left  behind 
us,  and  we  have  under  our  feet  a  coarse,  granular  mass 
made  up  of  rounded  parts  of  about  the  size  of  a  walnut 
or  a  hazel-nut  ( Grletscherkorn)  ;  still  farther  up,  these 
disappear,  to  be  replaced  by  a  fine  grain;  and  finally  we 
arrive  at  a  point,  perhaps  9,000  feet  up  on  the  moun- 
tain, where  the  granular  ice  merges  into  the  granular 
snow  (firn  or  neve)  out  of  which  it  has  been  con- 
structed. This  is  nearly  the  full  aspect  of  the  glacier, 
and  it  represents  almost  all  that  belongs  to  any  other 
glacier.  (Plates  24,  25,  26.) 


SNOW  AND   GLACIERS.  73 

Our  brief  study  has  now  prepared  us  for  the  ques- 
tion :  How  is  the  glacier  formed  ?  The  process  is  a 
simple  one,  and  one  that  is  practised  to  an  extent  by 
every  street-boy  who  lives  in  a  region  where  snow  falls. 
In  making  so  simple  an  object  as  an  ice-ball,  we  do 
very  much  what  nature  does  to  make  a  glacier.  In  the 
first  place,  we  compact  the  snow  with  our  hands,  and 
secondly  warm  it  by  contact,  and  then  allow  the  water 
that  has  formed  from  the  partial  melting  to  freeze  the 
whole  solid.  This  is  the  ice-ball.  This  process  is  in  a 
general  way  repeated  in  the  making  of  a  glacier.  In 
most  regions  of  glaciation  the  snow  that  forms  the 
glacier  accumulates  in  an  extensive  mountain  hollow 
or  basin,  where  it  heaps  up  layer  upon  layer  with  every 
fresh  snowfall.  Commensurately  with  this  upward 
growth,  the  lower  layers  become  more  and  more  com- 
pressed, and  into  them  descends  a  certain  quantity  of 
"liquid"  moisture  which  has  been  liberated  through  the 
energy  of  the  sun's  rays.  With  the  return  of  the  cold 
evening  and  night,  the  whole  freezes  solid,  and  we  have 
the  first  ice  of  the  forming  glacier,  —  a  granular  mass, 
of  about  the  texture  of  coarse  sugar,  and  built  up  in  dis- 
tinct layers  (strata),  corresponding  more  or  less  closely 
with  the  different  beds  of  snow.  This  is  the  neve  or 
firn-ice,  built  up  in  the  neve  or  firn-basin  from  which 
the  glacier  issues,  and  which  usually  occupies  a  posi- 
tion considerably  above  that  of  the  snow-line.  When 
the  ice  has  become  sufficiently  massive  and  crowded  it 
is  gradually  pushed  out  of  this  basin,  and  then  begins 
the  long  and  tedious  journey  down  the  mountain  side, 
usually  in  a  formed  depression  or  valley,  which  is  the 
glacial  movement  or  flow.  (Plate  29,  Fig.  1.) 


74  THE  EARTH  AND  ITS   STORY. 

Compound  Glaciers  ;  Medial  Moraines.  —  Under  this 
name  are  properly  designated  those  ice-sheets  which 
have  been  formed  through  a  coalescence  of  two  or  more 
glaciers  flowing  in  independent  valleys  of  their  own ; 
in  such  cases  the  united  parts  usually  retain  their  own 
individual  positions  in  the  main  stream,  flowing  to- 
gether, but  not  in  a  heterogeneously  mixed-up  mass. 
The  lateral  moraines  of  contiguous  glaciers  become, 
however,  merged,  and  they  then  constitute  a  medial 
moraine;  as  many  as  ten  or  fifteen  such  medial  mo- 
raines are  found  in  some  glaciers,  .and  indicate  a  union 
of  as  many  streams.  (Plate  29,  Fig.  1  ;  Plate  24.) 


2. 

THE  PHYSIOGNOMY  OF  GLACIERS. 

1.  The  Aletsch  Glacier,  Switzerland,  showing  its  composite  structure  in  the  number  of 

medial  moraines. 

2.  Side  view  of  the  Fan  Glacier,  North  Greenland;  it  debouches  upon  a  flat  meadow- 

plain.    The  stratification  of  the  the  ice  is  well  marked. 


Plate  30. 


THE  ASPECT  OF  A  GLACIATED  REGION. 

1.  The  summit  of  the  Shawangunk  Mountains  ("  Sam's  Toint"),  N.Y.,  smoothed  and 

rounded  by  the  glacial  ice  of  the  Glacial  Period. 

2.  A  glaciated  expanse  of  rock  near  Halifax,  N.S.,  showing  parallel  glacial  striae. 


THE    WORK  OF  GLACIERS.  75 


CHAPTER   VI. 

THE    WORK    OF    GLACIERS. 

The  Flow  of  Glaciers.  —  It  is  to-day  well  established 
that  the  motion  or  flow  of  glaciers  is  principally,  if  not 
almost  entirely,  conditioned  by  the  force  of  gravity; 
the  ice-sheet,  squeezed  from  behind,  tends  steadily 
downward,  just  as  a  river  of  any  viscous  substance 
would  do.  It  yields  to  this  flow  largely  because  ice  is 
in  a  measure  plastic,  and  permits  itself  to  be  moulded 
and  drawn  over  the  face  of  intervening  obstacles ; 
hence  it  is  that  the  glacier  overcomes,  even  on  most 
moderate  slopes,  the  enormous  resistance  which  friction 
with  the  floor  of  the  valley  imposes  upon  it.  In  its 
own  general  flow,  different  parts  of  the  same  ice-stream 
move  with  different  velocities ;  the  top  layers  move 
more  freely  than  the  lower  ones,  which  are  hard-pressed 
against  the  bottom,  and  the  central  portions  more 
rapidly  than  the  lateral  ones,  which  are  retarded  by 
scraping  along  the  mountain  sides.  This  irregular 
movement  causes  "  shearing "  of  the  ice,  layers  being 
tossed  up,  over,  and  above  one  another,  accompanied 
perhaps  by  an  endless  number  of  breakages.  A  large 
portion  of  both  the  longitudinal  and  the  transverse 
fissures  is  the  result  of  unequal  strain  brought  about 
in  this  uneven  flow;  and  were  it  not  for  the  property 
that  ice  possesses  of  repairing  itself,  —  regelation^  when 


76  THE  EARTH  AND  ITS   STORY. 

smooth  surfaces  are  brought  together  at  about  the  ten> 
perature  of  melting,  —  the  glacier  would  be  even  much 
more  rent  asunder  than  it  really  is.  When  rounding 
a  sharp  curve  the  glacier  tears  on  the  outer  side  and  is 
compacted  on  the  inner,  and  this  process  may  reverse 
itself  a  number  of  times  on  opposite  sides.  In  a  gen- 
eral way  the  flow  conforms  largely  to  the  laws  which 
gov-ern  the  flow  of  liquids  and  half-solids,  the  viscosity 
of  the  ice  being  an  alternative  to  the  freely  moving 
globules  or  particles  of  water. 

The  Rate  of  Glacial  Movement.  —  The  rate  of  flow 
depends  upon  a  number  of  special  conditions,  the  most 
potent  of  which  are  :  the  bed,  the  mass  of  the  ice,  and 
the  temperature  or  the  atmosphere.  Other  conditions 
being  equal,  the  flow  is  most  rapid  on  a  steep  slope, 
when  the  volume  of  the  ice  is  greatest,  and  when  the 
temperature  of  the  air  is  highest.  It  is  more  rapid  in 
summer  than  in  winter,  in  the  warm  hours  of  the  clay 
than  in  the  cold  of  night.  Again,  the  flow  is  faster 
in  the  top  ice  of  the  glacier  than  in  the  bottom  ice  — 
hence  the  overhanging  termination  which  is  often  found 
—  and  in  the  centre  than  on  the  sides ;  to  the  latter 
circumstance  is  due  the  frequently  curved  or  fan-shaped 
front  of  the  ice-sheet.  The  stream  compresses  itself  in 
narrow  courses  of  its  journey,  and  spreads  laterally  in 
opening  plains  and  valleys.  In  the  greater  number  of 
the  Alpine  glaciers  the  rate  of  the  fastest  flow  hardly 
exceeds  two  to  three  feet  per  day,  and  very  frequently 
it  does  not  even  reach  half  of  this  amount.  In  hard 
winters  the  flow  at  times  almost  ceases ;  on  the  other 
hand,  a  few  instances  are  recorded,  as  in  the  case  of  the 
Vernagt  Glacier,  in  1845,  where  the  advance  of  the  ice 


THE  WORK  OF  GLACIERS.  77 

covered  between  thirty  and  forty  feet  in  the  period  of 
twenty-four  hours.  Nearly  all  the  glaciers  of  the  world 
that  have  been  so  far  studied,  whether  of  the  Caucasus, 
the  Himalaya,  the  Andes,  or  of  Scandanavia,  are  slowly 
moving  ones.  In  or  toward  the  Arctic  regions  there 
is  a  tendency  to  accelerated  motion ;  and  if  we  are  to 
credit  fully  the  observations  that  have  been  made  in 
some  of  the  largest  glaciers  of  Greenland  (Jakobs- 
haven),  there  must  be  an  advance  in  those  parts  of 
sixty  to  seventy  feet  per  day ;  at  the  same  time  it  is 
certain  that  the  greater  number  of  the  Greenland  gla- 
ciers, whether  large  or  small,  have  only  the  motion  of 
the  glaciers  of  Switzerland. 

Glacial  Scour  and  Polish;  Roches  Moutonn£es.  —  It 
can  hardly  he  conceived  that  so  massive  a  body  of  ice 
as  is  represented  in  a  glacier  could  slide  over  its  bed 
without  putting  to  some  extent  its  impress  upon  it. 
It  rubs  over  the  rocks,  grooves  and  scratches  them  with 
the  small  pebbles  that  lie  frozen  in  the  under  surface 
of  the  ice,  and  it  probably  even  does  a  certain  amount 
of  direct  excavation  or  "scraping  out."  All  this  is 
known  as  the  work  of  the  glacier,  and  its  measure  is  a 
fair  index  of  the  size  of  the  ice-sheet  that  brought  it 
about.  The  greater  number  of  the  grooves  or  strise 
naturally  follow  in  the  line  of  movement  of  the  ice- 
flow,  and  are  therefore  more  or  less  parallel  with  one 
another.  (Plate  30.)  Those  of  the  ordinary  kind, 
perhaps  hundreds  of  feet  in  length  without  a  break, 
have  a  width  of  barely  more  than  an  eighth  or  quarter 
of  an  inch,  looking  like  pencil  furrows ;  elsewhere  they 
expand  into  grooves  of  from  one  to  three  feet  in  width, 
or  even  more,  or  make  distinct  flutings  in  the  rock. 


78  TUE  EARTH  AND  ITS   STOBY. 

Through  shearing  of  the  ice,  or  through  a  cross-flow, 
these  striae  may  be  made  to  cross  one  another,  and 
thereby  produce  a  puzzling  sculpturing  of  the  rock 
surface.  It  is  not  only  the  bed-rock  that  is  striated  in 
this  manner,  but  the  feature  belongs  to  the  overlying 
bowlders  as  well;  hence  we  have  a  distinctive  mark 
or  character  impressed  upon  the  true  "  glacial  bowlder," 
by  which  it  can  in  most  cases  be  easily  recognized. 

In  association  with  the  striating  and  rubbing  of 
rock-masses,  there  is  not  infrequently  a  pronounced 
"polishing,"  the  surface  being  ground  and  rubbed  so 
smooth  as  to  show  an  almost  mirror-like  texture.  Even 
the  hardest  rocks  may  be  rubbed  perfectly  smooth ; 
at  times  they  are  left  with  an  even  and  nearly  hor- 
izontal surface ;  at  other  times  they  are  ground  into 
a  series  of  hummocky  swellings,  or  mammillations, 
the  rocJies  moutonnees  of  the  glaciated  landscape. 
(Plates  30,  31.)  By  many  geologists  the  very  troughs 
or  valleys  which  the  glaciers  themselves  occupy  are 
assumed  to  have  been  worn  by  a  slow  but  continuous 
ice-action,  extending  certainly  over  thousands  of  years ; 
and  even  the  great  lakes  which  lie  by  or  near  these 
valleys,  like  many  of  the  lakes  of  Switzerland,  are  by 
some  attributed  in  their  formation  to  glacial  scour. 
And  there  is  really  much  to  support  this  view,  even  if 
it  cannot  be  said  to  be  as  yet  definitively  proved ;  for  it 
is  certain  that  the  form  of  the  glacial  valley  is  usually 
quite  different  from  the  valley  worn  by  simple  water- 
action,  —  being  flatter  and  with  a  broader  base,  —  and 
that  a  surprisingly  large  number  of  lakes  are  to-day 
found  in  regions  of  actual  glaciation,  or  of  glaciation 
which  culminated  in  a  geologically  recent  period.  Some 


THE   WORK  OF  GLACIERS.  79 

geologists  have  attempted  to  deny  to  the  glacier  all 
excavating  power,  asserting  that  no  glacier  of  to-day 
can  be  seen  working  in  this  way,  while  many  even  of 
the  larger  ice-streams  pass  over  loose  earth  and  grassy 
patches  without  materially  disturbing  either  the  one 
or  the  other.  There  is  no  questioning  this  condition ; 
but  it  is  an  exceptional  one,  and  the  fact  that  the  ice 
smooths  off  and  rounds  over  the  rock-surfaces  upon 
which  it  passes,  is  a  clear  indication  that  it  must 
do  some  excavating,  however  small  or  insignificant. 
Again,  however  unimportant  this  work  may  appear, 
by  multiplying  it  through  a  long  number  of  active 
years  of  work,  an  astonishingly  large  result  may  be 
reached.  Thus,  if  we  assume  that  the  ice  excavates 
only  the  one-twelfth  of  an  inch  per  day,  which  ordinary 
observation  could  not  detect,  by  the  amount  of  excava- 
tion in  the  short  period  of  one  hundred  years  would 
be  a  hollow  two  hundred  and  fifty  feet  in  depth,  and  in 
a  thousand  years,  twenty-five  hundred  feet,  far  greater 
than  the  depth  of  the  deepest  of  the  Alpine  lakes. 
This  would  easily  make  it  possible  that  the  largest 
of  the  rock-basins  have  been  made  through  glacial 
scour,  the  work  of  glaciers  no  longer  existent,  or 
of  such  as  are  to-day  merely  the  remains  of  former 
greatness. 

Drift.  —  Under  this  name  geologists  usually  class 
the  various  forms  of  deported  material,  the  bowlders, 
pebbles,  and  sands,  which  lie  in  the  path  of  the  mov- 
ing ice,  or  mark  the  passage  of  ice  that  formerly  ex- 
isted in  a  region  and  has  since  disappeared  (ancient 
glacier).  It  therefore  comprises  the  erratics  which 
have  already  been  described.  There  are  ordinarily  two 


80  THE  EAETH  AND  ITS   STORY. 

forms  of  drift  recognized,  a  high-level  and  a  low-level 
drift,  each  of  which  marks  relative  positions  or  sites 
occupied  by  the  transported  material.  High  up  on 
the  mountain  slopes,  in  regions  of  past  glaciation,  we 
find  the  erratics  or  bowlders  of  high-level  drift,  while 
the  valleys  are  perhaps  deeply  buried  beneath  the 
materials  of  the  low-level  drift,  —  materials  which  the 
glacier  pushed  along  on  its  bed  as  the  ground  moraine 
(or  "  till  ").  To  this  latter  class  belong  the  pyramidal 
or  lenticular  mound-like  hills  of  sand  and  cobbles,  so 
distinctive  of  the  landscape  of  many  glaciated  regions, 
and  known  as  udrumlins,"  "  kames,"  and  "  eskers," 
some  of  which  lie  longitudinally  in  the  course  of  move- 
ment of  the  glacier,  others  transversely  to  it.  The 
precise  method  of  their  formation  has  not  yet  been 
determined ;  although  it  seems  likely  that  some  of 
them,  at  least,  were  an  underwash  into  cavities  or  hol- 
lows of  the  ice. 

The  Retreat  of  Glaciers.  —  Probably  every  region  of 
glaciation  has  periods  of  most  active  movement,  when 
the  ice-sheets  are  more  steady  in  their  advance  than  at 
other  times,  and  reach  a  prolonged  maximum  exten- 
sion. Such  periods  of  advance  may  be  protracted  over 
a  goodly  number  of  years,  and  are  then  usually  fol- 
lowed by  periods  of  retreat,  not  necessarily  of  equal 
length.  In  such  periods  of  abatement  the  intensity  of 
the  lower  temperature  has  melted  off  more  ice  than 
was  furnished  to  the  glacier  from  above.  Most  of  the 
Alpine  glaciers,  up  to  within  the  last  few  years,  had 
for  a  decade  or  more  been  on  the  retreat,  and  some  of 
them  very  rapidly  so.  Necessarily,  when  this  recession 
takes  place,  the  ice  separates  (recedes)  from  its  terminal 


THE  WORK  OF  GLACIERS. 

1.  A  rock-surface  planed  by  glacial  passage  (indicated  by  the  arrows),  with  rock-islet 
(nunatak)  around  which  the  ice  moved  (outer  Duck  Islands,  off  Greenland). 

».  The  roches-moutonne'es  of  the  Grimsel,  Switzerland  —  the  rounded  and  polished 
rock-surfaces  showing  glacial  scour. 


Plate  32. 


THE  WORK  OF  GLACIERS. 

1 .  The  hummock  "  short  hills  "  of  a  portion  of  the  great  moraine  of  Pennsylvania. 

2.  Section -of  a  moraine  near  Whitewater,  Wisconsin. 


THE   WORK  OF  GLACIERS.  81 

moraine,  and  leaves  it  standing  in  marked  isolation,  — 
a  landmark  of  former  occupancy  by  the  ice,  now,  per- 
haps, removed  from  it  by  a  full  half-mile  or  more. 
The  glacier  had  in  the  meantime  constructed  for  itself 
a  new  moraine,  denning  as  before  the  termination  of 
the  ice-sheet.  In  valleys  of  considerable  recession  we 
frequently  meet  with  as  many  as  six  or  eight  transverse 
moraines  placed  at  irregular  intervals  back  of  one  an> 
other,  each  one  marking  a  temporary  pause  in  the 
almost  continuous  drawing  back  of  the  ice. 

Distribution  and  Dimensions  of  Glaciers. -- The  re. 
gions  of  most  extensive  glaciation  at  the  present  time 
are  to  be  found  in  the  Arctic  and  Artarctic  zones ; 
Greenland  is  buried  beneath  an  ice-cap  which  radiates 
off  hundreds  or  thousands  of  glaciers  into  the  water- 
areas  by  which  it  is  surrounded,  and  much  the  same 
condition  appears  to  prevail  over  what  is  commonly 
designated  the  Antarctic  continent.  Following  these 
polar  tracts  in  the  extent  of  their  glaciation,  are  the 
Himalaya  Mountains,  the  Alaska  region  (Muir  Gla- 
cier), Alps,  Caucasus,  Scandinavian  Alps,  Andes,  and 
the  North  American  Cordillera  (Selkirk  Mountains), 
etc.  Some  of  the  extinct  or  semi-extinct  volcanic 
cones  of  the  United  States  (Tacoma,  Shasta,  etc.)  bear 
on  their  summits  glaciers,  although  of  not  very  great 
extent.  Among  oceanic  islands,  —  barring  those  of 
the  Antarctic  tract,  —  Spitzbergen  (Dove  Glacier)  and 
New  Zealand  (Great  Tasman  Glacier)  have  probably 
the  largest  glaciers.  The  largest  authenticated  glacier 
of  to-day  is  the  Humboldt  Glacier,  which  discharges  into 
Smith  Sound,  off  the  north-west  coast  of  Greenland, 
with  a  frontage  said  to  be  sixty  miles  in  length.  The 


82  THE  EARTH  AND  ITS   STORY. 

northern  shore  of  Melville  Bay  is  seemingly  a  continu- 
ous glacier  for  at  least  thirty  miles.  The  Biafo  Glacier 
of  the  Himalayas  measures  about  forty  miles  in  length, 
the  Muir  Glacier  of  Alaska  probably  thirty  miles,  and 
the  Aletsch,  the  largest  of  the  Alpine  glaciers,  about 
thirteen  miles  (inclusive  of  its  upper  snow-field).  In 
some  of  these  glaciers  the  ice  is  not  less  than  300  to 
400  feet  thick ;  indeed,  Agassiz  had  assumed  that  the 
thickness  of  the  Aar  Glacier  of  Switzerland  was  at 
least  800  feet.  It  is  not  impossible  that  some  of  the 
Antarctic  glaciers  measure  2,000  to  3,000  feet  in  thick- 
ness, or  even  more;  but  such  a  development  of  ice  has 
not  yet  been  proved  to  exist. 

.Evidences  of  Past  Glaciation ;  Great  Ice  Age.  —  All 
over  the  north  of  Europe,  extending  southward  to 
about  the  49th  parallel  of  latitude,  we  have  in  the 
scattered  drift,  in  the  polished  and  striated  rock-sur- 
faces, evidences  of  former  possession  by  the  ice  where 
ice  no  longer  remains.  A  large  part  of  the  North 
German  plain,  of  Central  Russia,  etc.,  with  parts  of 
Great  Britain,  speak  plainly  the  evidence  of  past 
glaciatiori ;  and  the  character  of  many  of  the  trav- 
elled bowlders  shows  them  to  have  come  from  the 
north,  from  the  Scandinavian  Peninsula.  The  low- 
land plains  of  Switzerland,  the  eastern  heart  of  France, 
the  north  of  Italy,  speak  equally  of  a  glaciation  which 
was  far  more  extensive  than  the  glaciation  that  to-day 
characterizes  the  Alps ;  but  in  this  southern  glaciation, 
which  appears  to  have  been  contemporaneous  with  that 
of  the  north,  we  see  only  an  expansion  of  the  existing 
glaciers  of  the  Alpine  system ;  some  of  them  extended 
thirty,  forty,  or  even  fifty  miles  beyond  their  present 


THE    WORK  OF  GLACIERS.  83 

limits ;  indeed,  the  Rhone  glacier,  of  which  we  have  but 
a  fragment  remaining,  appears  to  have  travelled  quite 
to  the  outskirts  of  Lyons,  in  France,  a  distance  of  full 
two  hundred  miles.  During  this  period  of  excessive 
Alpine  glaciation,  when  possibly  the  mountains  were 
raised  thousands  of  feet  above  their  present  summits 
(and  in  this  way  accumulated  the  necessary  snows  to 
make  these  huge  ice-sheets),  the  lowland  of  Switzer- 
land was  covered  by  ice,  thousands  of  feet  in  thick- 
ness, which  filled  in  the  valleys,  and  distributed  its 
bowlders  high  up  on  the  distant  mountain  flanks. 

Even  more  extensive  are  the  traces  of  similar,  and 
not  improbably  simultaneous,  glaciation  on  the  North 
American  continent.  The  area  of  drift,  of  bowlders, 
sand,  striated  and  polished  rock-surfaces,  occupies 
most  of  British  North  America  east  of  the  Cordilleras, 
and  descends  into  the  United  States  to  the  40th  and 
39th  parallels  of  latitude.  Over  the  whole  of  New 
England,  nearly  to  the  tops  of  the  highest  mountain 
summits,  across  the  State  of  New  York  and  into  north- 
ern New  Jersey,  Pennsylvania,  and  central  Ohio,  and 
westward  beyond  the  Mississippi  River  in  Minnesota, 
are  distributed  in  various  forms  the  traces  of  this  won- 
derful visitation  of  ice,  the  exact  nature  of  which  is 
not  yet  fully  understood.  By  some,  this  ice  has  been 
looked  upon  as  being  a  united  and  single  sheet;  by 
others,  and  probably  with  more  reason,  as  a  union  of 
more  or  less  confluent  ice-sheets  or  distant  glaciers,  to 
all  of  which,  within  the  domain  of  the  United  States, 
a  southern  or  southerly  direction  had  been  given.  The 
striae  point  south-eastward,  southward,  and  south-west- 
ward, radiating  out  in  fan  form  from  the  region  of  the 


84  l  THE  EARTH  AND  ITS   STORY. 

Canadian  boundary.  Further  to  the  north,  in  Canada, 
Labrador,  the  Northwest  Provinces,  and  Newfoundland, 
the  striations  point  poleward  in  the  main.  Seemingly, 
therefore,  a  starting-point  for  both  north  and  south 
movements  must  have  been  somewhere  about  the  tract 
which  is  commonly  designated  the  Height  of  Land. 
Possibly  in  this  great  glacial  period,  or  Ice  Age  as  it 
is  commonly  designated,  the  mountains  stood  much 
higher  than  they  do  to-day,  and.  not  improbably  a 
considerable  portion  of  the  continent  itself  stood 
higher. 

The  Great  Terminal  Moraine.  —  Geologists  have  des- 
ignated under  this  name  a  vast  rampart-like  series  of 
undulations,  composed  of  pebbles,  sand,  and  bowlders, 
which  extends  with  almost  full  continuity  from  the 
Atlantic  border  of  the  United  States,  —  through  Cape 
Cod,  the  Vineyard  Islands,  Long  Island,  etc.,  —  west- 
ward to  the  Mississippi  River,  and  with  a  north-west- 
ward deflection  into  Canada,  and  seemingly  marks  the 
southern  limit  of  flow  of  the  continental  ice.  This 
moraine,  assumed  to  be  the  correspondent  of  the  termi- 
nal moraines  of  ordinary  glaciers,  rises  over  mountain 
ridges,  and  descends  across  valleys,  here  and  there 
broken  down  to  water-level,  and  elsewhere  washed 
away  by  the  streams  that  break  through  it,  arid  that 
convey  still  farther  southward  the  debris  as  part  of 
their  sediment.  In  places  this  moraine  rises  from  eighty 
to  one  hundred  and  fifty  feet  or  more,  and  its  peculiar 
"  short  hills  "  impress  a  distinct  individuality  upon  the 
landscape  of  which  they  form  a  part.  Numerous  small 
lakes,  ponds,  and  tarns  occupy  its  hollows,  or  "  kettle- 
holes,"  as  "  moraine  lakes."  It  has  now  been  pretty 


THE    WORK   OF  GLACIERS.  85 

well  established  that  this  so-called  terminal  moraine 
has,  at  least  in  part,  a  double  construction,  and  repre- 
sents a  partial  retreat  and  re-advance  of  the  ice ;  but 
there  is  no  evidence  that  two  distinct  ice  ages  were 
involved  in  its  making.  Several  of  the  large  northern 
lakes  (Michigan,  Erie,  Ontario)  are  outlined  by  mo- 
rainic  "lobes,"  and  it  is  certain  that  the  basins  of  all  of 
these  were  occupied  by  glacial  ice  ;  but  to  what  extent 
the  ice  was  instrumental  in  shaping  these  basins,  as  well 
as  the  basins  of  the  almost  endless  number  of  lakes  in 
Maine,  New  York,  Minnesota,  etc.,  which  are  found  in  the 
glaciated  tract,  remains  to  be  determined.  (Plate  32.) 
Cause  of  the  Great  Ice  Age.  —  Nothing  positive  is 
known  regarding  the  causes  which  brought  about  this 
vast  accumulation  of  ice.  By  some  physicists  the  oc- 
currence is  attributed  to  purely  astronomical  conditions, 
changes  in  the  relative  position  (as  to  nearness  or  dis- 
tance) of  the  earth  to  the  sun ;  and  by  others  to  a 
different  distribution  of  the  land  and  water-areas  of  the 
globe  than  that  which  is  to  be  found  at  the  present 
time.  The  subject  is  seemingly  too  remote  from  solu- 
tion to  require  discussion  in  this  place.  It  has  also  not 
yet  been  conclusively  demonstrated  whether  distinct 
glacial  periods  successively  repeated  themselves  in  past 
geological  history  or  not;  nor  do  we  know,  in  precise 
enumeration  of  years,  what  length  of  time  may  have 
elapsed  since  the  closing  of  the  period  which  is  com- 
monly designated  the  Ice  Age.  Man  was  certainly  an 
inhabitant  of  the  planet  during  some  of  its  existence, 
and  probably  long  antedated  it.  By  some  geologists 
the  disappearance  of  the  ice  is  assumed  to  have  been  no 
longer  ago  than  10,000  years  ;  by  others  it  is  placed  as 


86  THE  EARTH  AND   ITS   STORY. 

far  back  as  75,000  or  even  100,000  years.     One  fact 
is  clearly  established :   many  of  the  surface  features  of 
the  regions  that  were  formerly  occupied  by  the  ice  — 
the  river-gorges,  valleys,  etc.  —  have  been  carved  out 
since  its  disappearance. 

The  Niagara  Falls  and  gorge  of  the  Niagara  River 
have  frequently  been  taken  as  the  measure  of  time  by 
which  to  interpret  the  period  that  has  elapsed  since  the 
disappearance  of  the  ice.  But  the  length  of  time  in- 
volved in  the  cutting  of  the  gorge  is  in  itself  doubtful, 
and  has  been  variously  put  by  geologists  as  between 
7,500  and  35,000  years,  the  probability  inclining  in 
favor  of  the  longer  period.  The  uncertainties  that 
connect  themselves  with  calculations  of  this  kind  are 
too  numerous  to  permit  much  weight  to  be  attached  to 
a  general  result. 


THE    WORK   OF   UNDERGROUND    WATERS.          87 


CHAPTER    VII. 

THE    WORK    OF    UNDERGROUND    WATERS. 

Mineral  Waters.  —  The  fact  that  all  rock  is  more  or 
less  porous,  and  admits  of  the  passage  into  it  of  a  certain 
quantity  of  water,  is  sufficient  proof  that  every  portion 
of  the  earth's  surface  that  receives  rain  is  to  some  ex- 
tent invaded  by  underground  water.  This  condition  is 
directly  brought  to  our  notice  in  the  numerous  streams 
and  springs  that  issue  at  the  surface.  Some  of  these 
do  not  differ  essentially  from  the  streams  that  flow 
directly  over  the  surface  ;  others  have  become  impreg- 
nated with  the  earthy  materials  of  the  interior,  and 
have  thereby  become  converted  into  "  mineral  springs." 
As  such  we  recognize  a  number  of  distinct  types,  de- 
pending upon  the  special  mineral  substances  which  the 
waters  hold  in  solution.  For  example,  we  have  saline 
or  salt  springs,  which  contain  the  chloride  of  sodium,  or 
ordinary  salt,  in  solution ;  chalybeate  springs,  or  those 
which  are  largely  impregnated  with  iron ;  bitter  springs, 
which  contain  the  salts  of  magnesia  (Epsom  waters)  ; 
lime  springs  (like  those  of  Carlsbad),  which  hold  the 
carbonate  of  lime  ;  alum  springs,  soda  springs,  etc. 
The  quantity  of  foreign  material  thus  held  in  solu- 
tion differs  greatly,  and  is  necessarily  dependent  upon 
the  qualitative  structure  of  the  rock-masses,  upon  the 
length  of  course  of  the  underground  stream,  and  alsc 


88  THE  EARTH  AND   ITS   STORY. 

largely  upon  the  temperature  of  the  acting  water  —  the 
higher  the  temperature,  the  greater  its  solvent  power. 

The  Formation  of  Earth  Voids  ;  Caves.  — The  absorp- 
tion of  the  solid  materials  of  the  crust  by  underground 
waters,  and  their  carriage  to  the  surface,  mean,  neces- 
sarily, the  creation  of  internal  voids ;  these,  small  at  the 
start,  may  develop  into  great  expanses,  and  we  then 
have  the  formation  of  caves  and  rifts.  Especially  is 
this  the  case  in  limestone  regions,  and  to  a  less  extent 
in  regions  of  gypsum  deposits,  where  both  the  carbonate 
and  the  sulphate  of  lime  undergo  rapid  and  easy  solu- 
tion. All  the  really  great  caves  of  the  world  are  in 
limestone  rocks,  whether  they  are  of  marine  or  of  fresh- 
water origin  ;  i.e.,  whether  carved  out  by  the  oceanic 
waters,  or  worn  out  by  the  travel  of  underground 
streams.  Some  notion  of  the  prodigious  quantity  of 
material  that  is  brought  up  from  the  interior  through 
the  solvent  action  of  water  may  be  gathered  from  the 
fact  that  the  brine-spring  of  Neusalzwerk,  in  West- 
phalia, discharges  annually  a  quantity  of  common  salt 
that  is  the  equivalent  of  a  cube  of  seventy-two  feet 
dimensions,  and  in  addition  a  quantity  of  limestone  that 
would  make  a  cube  of  twenty-four  feet.  One  of  the 
warm  springs  of  Leuk,  Switzerland,  whose  temperature 
is  144°  F.,  has  been  estimated  to  discharge  annually 
nearly  9,000,000  Ibs.  of  gypsum,  or  the  equivalent  of 
60,000  cubic  feet.  The  potency  of  this  kind  of  work 
cannot  be  overestimated,  and  it  leads  to  the  easy  com- 
prehension of  the  manner  in  which  a  cave  is  formed. 

Among  the  largest  caves  of  the  world  are  the  Adels- 
berg  and  Aggtelek,  in  Austria-Hungary,  Weir's  and 
Luray  caves  in  Virginia,  the  Howe  cave  in  New  York, 


Plate  22. 


THE  WORK  OF  UNDERGROUND  WATERS. 

The  Hermannshohle,  in  the  Harz  Mountains,  Germany,  showing  stalactites  and 
stalagmites. 


Plate  23. 


-f— 


THE  WORK  OF  UNDERGROUND  WATERS. 

1.  Generalized  section-plan  of  a  cave :  The  bone-cave  of  Gailenreuth,  Bavaria,  showing 

the  relations  of  the  different  chambers. 
8.  Plan  of  Mammoth  Cave,  showing  the  courses  of  the  different  passages  (after  H.  C. 

Hovey). 


THE  WORK  OF  UNDERGROUND  WATERS.    89 

and  the  Mammoth  cave  of  Kentucky ;  the  last,  lying  in 
the  course  of  the  Green  River,  is,  in  the  direct  meas- 
urements of  its  passages,  probably  the  longest  of  all 
known  caves,  measuring  eleven  miles  or  more.  The 
height  of  many  of  the  chambers  exceeds  70-80  feet, 
and  exceptionably  it  reaches  200  or  even  250  feet 
(Mammoth  Dome),  the  connecting  passages  being 
usually  very  low.  (Plate  23,  Fig.  2.) 

Cave-Rifts  and  Bone-Caves.  —  These  structures  differ 
from  true  caves  mainly  in  their  contracted  areas  ;  in- 
stead of  expanding  out  into  roomy  chambers,  they  are 
more  generally  of  a  cleft  or  fissure  type,  abrupt  and 
tortuous.  Doubtless,  further  excavation  by  solvent 
water  would  in  course  of  time  convert  many  of  them 
into  true  caves.  In  some  cave-interiors  and  cave-rifts 
there  have  been  accumulated  extensive  deposits  of 
animal  remains,  mainly  the  skeletal  parts  of  extinct 
and  living  quadrupeds,  such  as  the  cave-bear,  cave-lion, 
rhinoceros,  mammoth,  mastodon,  hyena,  buffalo,  sabre- 
tooth  tiger,  giant  sloth,  etc.  Some  of  these  may  still 
be  living  in  the  region  where  the  special  cave  is  found ; 
elsewhere  they  have  been  removed  by  a  broad  migra- 
tion. Among  the  better  known  of  these  bone-caves  are 
those  of  Kirkdale,  Kent's  Hole,  and  Wookey,  in  Eng- 
land ;  Gailenreuth  in  Germany ;  and  Carlisle  and  Port 
Kennedy,  in  the  State  of  Pennsylvania.  How  these 
masses  of  remains  collected  in  the  cave-interiors  is  still 
a  question  of  probability,  and  perhaps  no  explanation 
is  suited  to  all  the  different  cases.  In  some  instances 
it  appears  certain  that  the  animals  to  whom  the  parts 
belonged  tumbled  in  accidentally  through  a  chance 
surface  opening;  elsewhere,  some  of  the  forms,  like 


90  THE  EAETH  AND   ITS   STORY. 

the  hyenas,  may  have  been  actual  cave-inhabitants, 
with  predatory  habits  that  brought  their  food-supply 
within  the  boundaries  of  their  habitations  ;  and  finally, 
in  many,  and  perhaps  in  most  instances,  the  accumula- 
tions have  followed  in  the  course  of  inundating  floods. 
It  is  in  these  bone-cave  deposits  that  there  have  been 
found  some  of  the  most  ancient  remains  of  man,  —  the 
Neanderthal  skull,  from  the  Neanderthal  Cave,  near 
Diisseldorf,  Germany,  the  "fossil  man"  from  the  cave  of 
Mentone  and  the  caves  of  Brazil,  —  and  with  them  some 
of  his  most  ancient  belongings  (chipped  implements, 
etc.).  None  of  the  bone-caves  appear  to  be  of  really 
great  antiquity,  although  their  existence  unquestion- 
ably covers  many  thousands  of  years.  (Plate  23,  Fig.  1 .) 

Natural  Bridges.  —  Closely  connected  with  cave-for- 
mation are  the  "  natural  bridges  "  which  span  chasms 
in  the  limestone  rock.  Many  of  these  are  unquestion- 
ably only  parts  of  cave-roofs,  which  have  remained 
standing  after  the  caves  themselves  have  disappeared 
through  natural  destruction.  Such  appears  to  be  the 
famous  Natural  Bridge  of  Virginia,  with  a  height  of 
215  feet,  a  span  of  60  feet,  and  a  thickness  of  rock  of 
40  feet. 

Stalactites  and  Stalagmites  ;  Ice-Caves.  -  -  Under 
these  names  we  understand  the  peculiar  and  frequently 
fantastic  deposits  of  lime  that  have  been  shed  by  the 
percolating  waters  of  caves.  They  dissolve  a  certain 
quantity  of  the  lime-carbonate  in  passing  through  the 
rock,  and  again  deposit  the  same  when  their  solvent 
power  has  been  measurably  reduced.  In  this  way  are 
formed  the  large  pendants  (stalactites*)  which  hang  from 
the  roof,  and  the  columnar  buttresses  (stalagmites) 


Plate  33. 


I 


THE  WORK  OF  HEATED  WATERS. 

1.  The  cone  of  Giant  Geyser,  Yellowstone  National  Park. 
8.  A  cone  of  a  hot-spring  in  the  Yellowstone  region. 


THE  WORK  OF  UNDERGROUND  WATERS.    91 

which  rise  from  the  floor.  The  various  forms  of  "  or- 
gan-pipes "  and  "  curtains  "  are  merely  modifications  of 
the  ordinary  stalactite  structure,  just  as  the  "  floor- 
crust  "  is  merely  a  variety  of  the  stalagmite.  (Plate 
22.)  The  vast  deposits  of  "  Mexican  onyx,"  so-called, 
are  stalagmitic  infiltrations  between  the  layers  of  regu- 
larly stratified  marine  strata.  In  this  connection  should 
be  mentioned  a  class  of  caves  which  differ  from  the 
ordinary  lime-crusted  ones  in  the  fact  that  the  interior 
deposits,  whether  as  floor-crusts,  stalactites,  or  stalag- 
mites, are  of  ice-formation  instead  of  carbonate  of  lime. 
Such  ice-caves  are  of  somewhat  frequent  occurrence  in 
the  mountains  of  Europe, — in  the  Alps,  Jura,  Carpa- 
thians, Urals ;  and  some  of  them  are  300  to  400  feet 
in  length,  with  a  height  of  chamber  of  100  feet  or  more. 
The  largest  of  these  caves  are  those  of  Kolowrat,  near 
Salzburg,  and  Dobschau,  in  northern  Hungary.  The 
manner  of  ice-formation  is  not  precisely  known :  in 
some  it  seems  to  be  an  accumulated  winter  deposit ;  but 
in  others  it  would  appear  as  though  the  freezing  took 
place  in  early  summer,  the  slow  percolation  of  melted 
waters  from  the  outside  finding  in  the  interior  a  suffi- 
ciently low  temperature  to  bring  them  to  a  condition  of 
freezing. 

Hot  Springs  and  Geysers.  —  Reference  has  already 
been  made  to  the  heating  up  of  waters  when  they  gain 
the  deep  interior  of  the  earth;  when  they  rise  to  the 
surface  with  a  marked  accession  of  temperature  they 
constitute  the  well-known  "  hot  springs."  The  ther- 
mal springs  of  Bath,  England,  have  a  temperature  of 
120°  F.,  which,  in  accordance  with  the  law  of  increase 
of  1°  F.  for  about  every  60  feet  of  descent,  would  indi- 


92  THE  EARTH  AND  ITS   STORY. 

cate  a  rise  from  a  depth  of  about  4,000  feet;  the  waters 
of  Chaude-Aigues,  in  France,  have  a  temperature  of 
178°,  which  indicates  a  depth  of  origin  of  at  least  7,000 
feet;  and  those  of  the  rivulet  of  Trincheras,  in  Vene- 
zuela, had  in  1823  a  temperature  of  206°.  The  forms 
of  hot  springs  known  as  geysers  differ  mainly  from  the 
ordinary  type  in  having  their  outflow  accompanied  by 
intermittent  or  paroxysmal  explosions  of  boiling  water 
and  steam.  In  its  general  structure  the  geyser  consists 
of  three  or  more  essentially  different  parts :  1,  the 
underground  irregular  course  of  the  spring-waters ;  2, 
a  vertical  conduit  of  varying  depth  through  which  the 
waters  pass  before  gaining  the  surface ;  and  3,  a  mound 
or  cone  (the  "  geyser  cone  "),  with  a  top-basin,  which 
has  been  built  up  of  the  siliceous  material  which  the 
stream  has  itself  deposited  at  its  point  of  exit  from 
the  earth.  The  vertical  conduit  just  referred  to  is  a 
central  passage  or  shaft  which  traverses  this  cone. 

The  explosions  which  characterize  geyser  action  are 
brought  about  as  the  result  of  two  conditions :  1,  re- 
sistance to  the  escape  of  imprisoned  steam  by  the  pres- 
sure of  the  column  of  water  contained  in  the  conduit ; 
2,  release  of  this  pressure  through  a  change  in  the 
equilibrium  between  the  acting  and  resisting  forces. 
The  greatest  development  of  geyser  action  is  to  be 
found  in  Iceland,  New  Zealand,  and  the  Yellowstone 
National  Park,  more  especially  in  the  last-named  re- 
gion. Among  the  better-known  geysers  of  this  tract 
are  the  "  Giant,"  whose  jet  is  sometimes  thrown  to  a 
height  of  200  feet,  and  whose  cone  measures  but  ten 
feet  in  height ;  the  "  Beehive,"  with  a  jet  of  200  feet, 
and  a  cone  of  three  feet;  the  "Liberty  Cap,"  whose 


THE  WORK  OF  HEATED  WATERS. 

1.  Crow's  Nest  Geyser.  New  Zealand,  in  eruption. 

2.  The  cone  and  terraces  of  Castle  Geyser,  Yellowstone  National  Park. 


THE  WORE:  OF  UNDERGROUND  WATERS.   93 

cone  measures  50  feet  in  elevation ;  and  the  "  Grand 
Geyser,"  which  plays  from  a  mound  measuring  50  feet 
in  diameter,  and  only  one  foot  in  height.  (Plates 
33,  34.) 

In  immediate  association  with  geyser  action  must  be 
classed  the  large  deposits  of  siliceous  and  calcareous 
sinter  which  are  precipitated  by  the  superheated  and 
highly  charged  Avaters  of  the  geyser  region,  and  in  some 
instances  form  most  picturesque  and  noble  features  in 
the  landscape.  The  travertine  terraces  of  Gardiner's 
River,  in  the  Yellowstone  region,  are  an  example 
of  this  kind;  and  still  more  noted  were  the  famous 
"Pink"  and  "White  Terraces"  of  Rotomahana,  New 
Zealand,  —  destroyed  by  the  eruption  of  Tarawera  in 
June,  1886,  —  which  in  beauty  and  scale  of  develop- 
ment far  surpassed  all  other  similar  structures,  and 
were  by  many  classed  among  the  wonders  of  the  worldo 
(Plate  35.) 


94  THE  EARTH  AND   ITS   STORY. 


CHAPTER   VIII. 

THE  RELATIONS  OF  THE  SEA  TO  THE  LAND  ;  OK  WHAT 
THE  SEA  DOES  AND  WHAT  IT  UNDOES. 

Configuration  of  the  Oceanic  Trough.  —  There  are 
many  who  even  today  believe  that  the  moment  you 
leave  the  continental  borders  you  almost  immediately 
step  out  over  the  great  deep  sea  — the  "unfathomable  " 
ocean.  They  may  have  heard  of  ships  grounding  miles 
away  from  shore,  may  have  seen  the  masts  of  the  ves- 
sels that  are  held  fast;  but,  beside  the  old  notion  of 
immediate  profundity,  these  direct  evidences  of  shallow- 
ness  carry  little  weight.  As  an  actual  fact,  the  border 
strip  of  the  greater  part  of  the  ocean  is  a  very  moder- 
ately shelving  plane,  dropping  so  gradually  that  in  sec- 
tions of  a  mile  the  fall  could  hardly  be  detected  by  the 
eye.  Off  the  east  coast  of  much  of  the  United  States, 
—  off  New  Jersey,  for  example,  —  the  seaward  slope 
for  a  length  of  some  seventy  miles  or  more  is  on  an 
average  not  more  than  seven  or  eight  feet  to  the  mile ; 
which  means  that  at  a  distance  of  fifty  miles  from  the 
land  the  depth  of  water  would  not  be  sufficient  to 
submerge  the  steeples  of  one  of  half  a  dozen  European 
cathedrals,  were  these  buildings  carried  out  to  sea  to 
the  distance  mentioned.  A  half-mile  away,  a  man 
could  in  places  wade  about  with  his  head  out  of  water. 
Qff  some  parts  of  the  Irish  coast  the  shallows  extend 


RELATIONS   OF  THE  SEA    TO   THE  LAND.         95 

still  farther  seaward,  dropping  on  an  average  six  feet 
per  mile  for  200  miles.  In  a  general  way  it  may  be 
said  that  this  oceanic  shallow,  or  " continental  shelf" 
as  it  is  most  commonly  called,  extends  out  from  fifty 
to  seventy-five  miles,  beyond  which  the  descent  of  the 
sea-bed  is  rapidly  more  abrupt.  In  a  horizontal  dis- 
tance of  ten  miles  it  may  fall  9,000  or  10,000  feet,  but 
even  this  is  not  that  stupendous  plunge  which,  in 
many  minds,  is  associated  with  the  oceanic  basins  ;  in 
fact,  there  is  hardly  a  slope  in  any  part  of  the  oceanic 
trough  —  except  perhaps  among  certain  coral  islands, 
or  among  the  islands  of  a  recently  broken-in  land-mass 
(as  is  represented  by  the  Grecian  Archipelago)  — 
which  could  not  be  readily  traversed  by  a  horse  and 
wagon. 

The  Origin  of  the  Oceanic  Trough.  —  Concerning  the 
origin  of  the  continental  shelf,  or  what  this  continental 
shelf  really  signifies,  there  is  little  to  be  said.  By 
some  it  is  assumed  to  have  been  built  up  from  the 
oceanic  depths  through  the  accumulation  of  sediment 
derived  from  the  destruction  of  the  continents ;  by 
others  it  is  conceived  to  be  part  of  the  continent  itself, 
at  the  present  time  submerged.  This  latter  •  interpre- 
tation is  probably  more  nearly  the  correct  one.  As  a 
question  in  physics,  there  is  not  one  more  interesting 
than  that  which  relates  to  the  origin  or  construction  of 
the  oceanic  basins  themselves.  The  questions :  How 
were  they  formed,  when  were  they  formed,  and  what 
will  become  of  them  ?  puzzled  geographers  and  geolo- 
gists more  than  a  half-century  ago,  and  they  still  con- 
tinue to  puzzle.  Perhaps  the  nearest  approach  to  a 
true  answer  to  the  question  of  origination  is  that  which 


96  THE  EARTH  AND  ITS   STORY. 

assumes  the  oceanic  troughs  to  be  parts  of  a  series  of 
giant  folds  —  of  which  the  continents  are  another  part 
—  made  when  the  earth  first  contracted  as  a  cooling 
mass ;  and  that  the  present  profound  depths  have  been 
brought  about  by  successive  breakages  or  subsidences 
of  the  ocean-floor.  At  any  rate,  it  is  nearly  certain 
that  we  are  correct  in  interpreting  the  oceanic  basins 
as  areas  of  weakness  in  the  crust,  a  weakness  which 
was  initial  with  the  first  making,  and  has  continued 
ever  since.  The  large  number  of  volcanic  disturbances 
which  take  place  in  various  parts  of  the  oceanic  abyss, 
around  and  in  the  numerous  islands  that  rise  out  of  it 
and  along  the  continental  border-line,  and  the  almost 
innumerable  earthquake  tremors  and  dislocations,  are 
facts  that  go  far  to  sustain  this  view,  even  if  they  do 
not  absolutely  prove  it.  Further,  there  is  reason  to 
believe  that  much  of  the  existing  basins,  Atlantic  and 
Pacific,  was  made  (geologically  speaking)  in  compara- 
tively recent  times,  although  some  parts  of  them  are 
doubtless  very  ancient. 

Permanency  or  Non-Permanency  of  Continents  and 
Oceans.  —  A  question  of  much  interest  that  has  from 
time  to  time  engaged  the  attention  of  geologists  is  that 
which  relates  to  the  permanency  or  non-permanency 
of  the  oceanic  troughs.  When  in  our  rambles  across 
country  we  come  upon  giant  rock-masses  that  protrude 
their  heads  through  a  crumbling  soil  or  the  smiling  car- 
pet of  grass  and  flowers,  we  know  that  in  those  rocks 
we  have  the  evidences  of  former  possession  by  the  sea. 
There  are  the  heavy  beds  of  limestone,  of  shale,  of 
sandstone  ;  there  are  the  impressions  of  the  life  that 
tenanted  the  seas  —  shells,  corals,  crinoids,  etc.  Here, 


RELATIONS   OF  THE   SEA    TO    THE  LAND,          97 

again,  is  this  vast  deposit  of  pudding-stone  or  shingle, 
the  veritable  beach-line  of  an  ancient  sea;  and  there 
the  marks  of  the  ocean's  ripples.  We  may  travel  from 
one  end  of  the  continent  to  the  other,  or  to  the  farther 
ends  of  any  continent,  and  from  the  sea-level  to  very 
nearly  the  highest  points  of  all  mountains,  and  we  shall 
almost  everywhere  find  conclusive  evidence  that  for- 
merly the  sea,  at  various  periods,  occupied  the  region 
over  which  we  are  travelling.  East  of  the  Alleghany 
Mountains,  west  of  the  Alleghany  Mountains  ;  east  of 
the  Rocky  Mountains,  west  of  the  Rocky  Mountains ; 
and  in  the  great  central  basin,  —  it  is  all  one  history, 
a  history  that  repeats  itself  in  England,  France,  Russia, 
China,  Australia,  everywhere. 

Of  one  fact  we  have  thus  made  certain:  the  conti- 
nents, at  least,  have  not  been  permanent.  They  have 
been  covered  by  the  water  of  the  ocean  once,  twice, 
several  times,  and  to  varying  depths  of  from  1,000  to 
5,000  feet,  and  not  improbably  of  even  8,000  to  10,000 
feet.  Whether  or  not  beneath  this  deep  covering  of 
water  they  were  then  marked  off  from  still  deeper 
oceanic  basins,  and  in  a  way  constituted  "  submerged  " 
continents,  or  continents  in  preparation,  cannot  now  be 
told,  although  many  have  argued  in  favor  of  such  a 
supposition. 

Disruption  of  Continental  Masses.  —  The  remaining 
part  of  the  inquiry  rests  with  the  sea  itself.  Have  its 
greatest  depths  always  been  depths  since  they  were 
first  formed,  or  has  the  ocean-floor  been  from  time  to 
time  elevated  high  and  dry,  and  again  as  often  de- 
pressed ?  To  this  question  no  positive  answer  can  be 
given,  but  probability  favors  the  view  that  the  greater 


98  THE  EARTH  AND   ITS    STORY. 

depths  have  been  steadily  or  progressively  getting 
deeper.  With  this  understanding  there  would  be  a 
certain  amount  of  permanency  established  for  the 
oceanic  basins;  but  this  supposition  in  no  way  asserts 
that  large  continental  areas  may  not  have  dropped  or 
subsided  within  the  troughs  that  to-day  belong  to  the 
sea.  The  North  and  South  Atlantic  basins  may  well 
have  been  in  existence  when  an  east-and-west  or  north- 
east-and-south-west  land  connection  still  united  the 
America  of  the  New  World  with  Europe  and  Africa  of 
the  Old.  There  are  many  reasons  for  believing  that 
this  was  actually  the  case.  Again,  it  is  certain  that  a 
large  Arctic  continent  has  been  shivered  up  and  lost 
beneath  the  waters  of  what  are  at  present  a  part  of  the 
Atlantic  and  the  Arctic  basins.  The  remnants  of  this 
continent  are  still  to  be  seen  in  the  lands  of  Greenland, 
Spitzbergen,  Nova  Zembla,  and  in  the  disjointed  tracts 
that  lie  north  of  the  American  continent.  In  the  Ant-- 
arctic realm  even  more  disruption  appears  to  have 
taken  place. 

Configuration  of  the  Atlantic  Basin.  —  The  existing 
conformation  of  the  Atlantic  trough  shows  it  to  be  a 
double  basin,  with  an  easterly  and  a  westerly  half,  be- 
tween which  runs  a  dividing  ridge  or  backbone,  whose 
top  parts  are  still  submerged  some  8,000  or  10,000  feet 
beneath  the  surface  of  the  waters.  This  longitudinal 
ridge  is  commonly  known  under  the  two  names  of  the 
"Challenger"  (for  the  southern  half)  and  "Dolphin" 
(for  the  northern  half)  ridges.  •  In  the  deeper  basins 
that  lie  on  either  side  of  this  ridge  a  depth  of  water  is 
frequently  found  of  15,000  to  17,000  feet,  increasing 
in  places  or  spots  to  20,000  and  even  25,000  feet ;  the 


RELATIONS   OF   THE   SEA    TO    THE  LAND.          99 

greatest  recorded  depth  of  the  Atlantic  is  27,366  feet 
found  some  sixty  miles  from  the  island  of  St.  Thomas 
What  the  depressed  ridge  of  the  middle  Atlantic 
means,  has  yet  to  be  determined;  some  have  argued 
with  much  plausibility  that  it  represents  a  sunken 
mountain  chain,  and  with  it,  perhaps,  a  sunken  conti- 
nent. The  fact  that  a  number  of  volcanic  islands  of 
the  Atlantic  are  perched  upon  this  ridge  as  steeply 
rising  volcanoes,  just  as  we  find  the  great  volcanic 
peaks  of  South  America  implanted  upon  the  mighty 
Andean  ridge,  carries  weight  in  this  connection;  but 
probably  it  does  not  quite  prove  the  case.  The  Pacific 
Ocean  has  no  such  defined  separating  backbone,  al- 
though it  has  a  number  of  very  distinct  submerged 
ridges  of  minor  extent,  usually  with  a  north-west  and 
south-er.st  trend,  which  carry  many  of  the  almost  innu- 
merable volcanic  and  coral  islands  and  islets  that  are 
scattered  about.  The  greatest  known  depth  is  29,200 
feet,  found  in  latitude  24°  S.,  very  nearly  due  south  of 
the  Friendly  Islands.  This  is  almost  ^exactly  the  equiv- 
alent of  the  highest  known  elevation  of  the  land-sur- 
face, Mount  Everest  in  the  Himalayas  (29,002  feet), 
but  this  correspondence  has  no  special  significance. 
The  average  depth  of  all  the  oceans  is  probably  in  the 
neighborhood  of  12,000  feet. 

Inconstancy  of  the  Ocean-Level ;  Oceanic  Trans- 
gressions and  Recessions.  —  It  is  customary  to  look 
upon  the  surface  of  the  sea  as  having  a  very  nearly 
uniform  level,  known  as  the  "level  of  the  sea,"  from 
which  our  ordinary  calculations  of  land-elevation  and 
sea-depression  are  made.  That  this  level  cannot  be 
uniform  for  all  parts  of  the  earth  becomes  evident  the 


100  THE  EARTH  AND   ITS   STORY. 

moment  we  consider  what  must  necessarily  result  from 
the  attracting  power  of  gravity.  All  bodies  attract  one 
another  in  degrees  proportional  to  their  masses ;  hence, 
the  sea  is  drawn  upon  all  sides  by  the  continental  but- 
tresses that  surround  it,  and  proportionally  to  the  sizes 
of  those  continents.  The  greater  in  bulk  the  conti- 
nent, the  greater  will  be  its  attracting  power;  and 
where  specially  large  mountain  masses  are  grouped 
about  certain  parts  of  continents,  there,  necessarily,  will 
be  localized  the  greatest  attracting  force.  Observations 
are  not  yet  in  accord  as  to  the  actual  deformation  of 
the  ocean-level  through  this  irregularly  acting  attrac- 
tion, but  it  has  been  assumed  by  some  that  it  might  in 
some  places  amount  to  as  much  as  2,000  or  4,000  feet. 
In  other  words,  the  surface  of  the  ocean  may  vary  in 
its  distance  from  the  earth's  centre  by  fully  this 
amount.  Whether  it  really  does  or  does  not  must  be 
left  for  more  accurate  researches  to  determine ;  but  for 
our  purposes  it  is  sufficient  to  know  that  a  variation  in 
level,  of  whatever  extent,  does  exist. 
,  Another  form  of  inconstancy  in  the  oceanic  waters 
is  brought  about  in  a 'different  way.  If,  through  what- 
ever cause,  a  considerable  part  of  the  oceanic  floor 
should  be  upheaved,  and  thereby  contract  the  space 
that  is  normally  occupied  by  the  oceanic  waters,  there 
must  necessarily  follow  a  displacement  of  these  waters, 
with  an  overflow  on  the  land ;  we  should  then  have  a 
deluge,  or  oceanic  transgression.  If,  on  the  other  hand, 
a  reversed  action  took  place ;  i.e.,  if  instead  of  rising, 
the  oceanic  floor  broke  still  farther  within  itself,  or  if, 
through  the  fall  of  an  adjacent  piece  of  continent,  the 
basin  was  expanded  laterally,  —  a  condition  that  must 


RELATIONS   OF   THE   SEA    TO    THE  LAND.       101 

have  been  imposed  upon  the  Atlantic  at  the  time 
when  the  Mediterranean  area  subsided,  —  then,  of  ne- 
cessity, must  there  have  been  a  contrary  movement  in 
the  ever  mobile  waters.  With  a  basin  of  enlarged 
capacity  to  receive  them,  they  will  withdraw  from  the 
land,  and  leave  high  and  dry  that  which  has  before 
been  covered ;  this  condition  has  properly  been  called 
an  oceanic  recession.  These  are  important  facts  to  real- 
ize, since  they  open  up  a  conception  in  geological  his- 
tory very  different  from  the  ideas  .that  were  generally 
held  by  the  older  geologists.  They  indicate  that  the 
evidences  that  have  ordinarily  been  received  as  prov- 
ing movements  of  the  land  in  and  out  of  the  water 
may  at  times,  and  perhaps  most  often,  have  been  in 
reality  only  the  proofs  of  water-movements,  and  that 
the  waters  cover  a  perfectly  stable  land-surface. 

Drowned  Lands  and  Waters.  -  -  When  a  land  area, 
of  whatever  extent,  becomes  submerged  beneath  the 
oceanic  waters,  whether  through  its  own  subsidence,  or 
through  a  rise  in  the  level  of  the  sea  (oceanic  trans- 
gression), it  becomes  properly  a  drowned  land.  Pieces 
of  drowned  land  are  familiar  objects  to  the  inhabitants 
of  many  portions  of  the  eastern  border  of  the  United 
States,  and  perhaps  most  so  in  the  State  of  New  Jersey, 
where  the  encroaches  of  the  sea  have  been  carefully 
studied  and  plotted.  Patches  of  meadow-land  lie  here 
and  there  covered  by  the  sea,  and  in  places  the  remains 
of  the  old  foresters  can  still  be  seen  rising  out  of  the 
invading  waters.  The  same  condition  is  to  be  found 
along  many  parts  of  the  British  coast,  in  the  south  of 
the  Scandinavian  peninsula,  along  the  Bay  of  Fundy, 
etc.  A  large  portion  of  the  lowlands  of  Belgium  and 


102  THE  EARTH  AND   ITS   STORY. 

the  Netherlands  would  be  drowned  lands  were  they 
to  be  deprived  of  their  protecting  dykes,  since  they 
occupy  a  level  that  is  actually  lower  than  that  of  the 
sea.  How  far  the  submergence  in  these  cases  was 
brought  about  by  a  positive  movement  of  subsidence 
on  the  part  of  the  land,  or  through  an  oceanic  trans- 
gression, remains  yet  to  be  determined.  In  the  absence 
of  a  knowledge  that  will  permit  us  to  determine  a 
question  of  this  kind,  it  has  been  found  convenient  to 
use  the  terms  "submergence"  and  "apparent  subsi- 
dence," in  preference  to  simple  subsidence,  to  indicate 
for  the  land  its  lower  placement  relative  to  the  sea. 

The  continental  shelf,  as  has  already  been  stated,  is 
by  many  geologists  considered  to  be  a  submerged  ex- 
tension of  the  continent  which  it  immediately  adjoins. 
A  certain  amount  of  strong  evidence  supporting  this 
view  is  found  in  the  fact  that  over  parts  of  this  shelf 
deep  furrows  find  their  way  in  more  or  less  regular 
lines  to  the  deeper  sea,  and  landward  connect  with 
estuaries  of  existing  rivers.  One  such  is  found  con- 
tinuing oceanward  from  the  mouth  of  the  Hudson 
River  for  one  hundred  and  eighty  miles  or  more,  and 
marked  off  not  far  from  its  termination  by  a  depth  of 
its  own  of  some  eighteen  hundred  feet.  Another  con- 
tinues the  estuary  of  the  Delaware ;  and  still  others, 
perhaps  less  positive  in  their  relations,  are  believed  to 
represent  the  St.  Lawrence  and  Susquehanna.  These 
sub-oceanic  furrows,  seeing  how  closely  they  stand  in 
relation  with  the  land-waters,  have  naturally  been  as- 
sumed to  be  of  river  formation,  and  to  have  been  made 
at  a  time  when  the  rivers,  with  greater  extension  ocean- 
ward,  were  flowing  over  dry  land,  and  with  a  fall  suf- 


RELATIONS   OF  THE  SEA    TO    THE  LAND.       103 

ficient  to  excavate  the  deep  channels.  If  this  is  their 
true  interpretation,  then  they  are  strictly  "drowned 
channels."  We  are  probably  even  justified  in  consid- 
ering the  long  tidal  reaches  of  some  of  our  rivers  as- 
"drowned  rivers;"  for  they,  too,  have  seemingly  been 
invaded  by  the  sea.  The  lower  course  of  the  Hudson, 
for  some  sixty  to  seventy  miles  above  its  mouth,  flows 
over  a  drowned  channel,  for  the  river  of  itself  could 
hardly  have  excavated  below  sea-level;  and  the  chan- 
nel that  it  now  occupies,  with  a  depth  of  fifty  or  sixty 
feet,  must  have  been  cut  when  it  stood  at  a  level  above 
that  of  the  sea.  The  same  is  true  of  the  estuary  of 
the  Delaware  and  of  the  Susquehanna,  and,  in  fact,  of 
every  stream  the  depth  of  which  is  considerably  greater 
than  that  of  the  outlying  waters. 

Fjords  ;  Strands  and  Ocean  Terraces.  —  One  of  the 
most  marked  characteristics  of  northern  border-lands  is 
the  number  of  rock  and  mountain  prominences  which 
project  into  the  sea,  and  include  between  themselves 
continuations  of  land- valleys  —  the  fjords.  The  coasts 
of  the  Scandinavian  peninsula  and  Britain  (particu- 
larly of  Scotland),  of  Maine,  Newfoundland,  Labrador, 
and  Greenland  are  distinguished  by  fjord  ("frith," 
"firth")  structure.  In  most  cases,  probably,  the  fjord 
is  merely  a  submerged  mountain  valley ;  for  in  all  its 
special  characteristics  it  bears  the  imprint  of  the  valley 
that  continues  it  on  the  land.  Soundings,  too,  indicate 
a  gradual  continuance  of  the  floor  of  the  land-valley 
beneath  the  sea,  or  into  that  portion  which  is  strictly 
drowned.  Most  fjord-valleys  appear  to  have  been 
fashioned  more  or  less  extensively  by  glacial  ice,  a 
circumstance  that  explains  why  by  far  the  greater  num- 


104  THE  EARTH  AND   ITS   STORY. 

ber  of   fjords   occur  in    regions   of    existing  and   past 
glaciation. 

In  evidence  of  the  relative  rise  of  the  land  are  the 
numerous  elevated  ocean  beaches  or  "  terraces"  which  ac- 
company certain  coast-lines.  These  are  the  counterparts 
of  the  terraces  that  we  have  found  to  border  inland 
lakes,  and  they  tell  the  same  history  of  a  withdrawal  or 
lowering  of  the  waters.  Marine  terraces  frequently 
occur,  four,  five,  or  six,  placed  one  above  the  other ;  and 
they  usually  follow  with  marked  horizontality  the  sur- 
face level  of  the  sea.  They  are  the  ancient  beaches,  and 
to  the  highest  of  them  the  ocean  at  one  time  reached; 
in  some  regions  they  constitute  the  country  roadways, 
and  are  known  as  "  strands."  (Plate  21,  Fig.  2.) 

Wear  of  the  Shore-Line ;  Plain  of  Marine  Denuda- 
tion. —  Wherever  the  waves  and  cutting  surf  impinge 
upon  the  shore-rocks,  they  begin  the  work  of  destruc- 
tion; and  this  work  continues  until  the  land-surface 
has  been  reduced  to  the  form  which  makes  the  "bite" 
of  the  waves  no  longer  possible.  So  long  as  cliffs  or 
bluffs  remain,  the  sea  continues  mercilessly  to  batter 
them  down ;  they  are  undercut  and  toppled  over,  ham- 
mered into  by  the  flying  fragments  of  rock  that  the 
sea  itself  tosses  up,  or  wedged  apart,  where,  in  narrow 
sluice-ways  or  races  ("  ovens,"  "  kitchens,"  "  blow- 
pipes," and  "  blow-holes  ")  the  surging  waters  acquire 
increased  violence.  Everything  yields  sooner  or  later ; 
and  the  sea  follows  its  conquest  by  quietly  levelling  all 
to  the  ignoble  form  of  a  gently  undulating  plain,  —  the 
plain  of  marine  denudation.  Far  into  continental  ter- 
ritories these  plains  of  denudation  extend,  and  teach 
us  the  lesson  of  oceanic  transgressions  and  recessions. 


Plate  21. 


OCEANIC   DKSTKUCTIOX. 


1.  Marine  arches  on  the  northern  coast  of  Ireland,  the  work  of  to-day. 

2.  The  island  of  Torghatten,  west  coast  of  Norway,  with  a  blow-hole  cut  through  the 

rocks  by  the  wash  of  the  sea.     The  hole  is  now  upwards  of  400  feet  above  sea- 
level,  and  thus  indicates  a  disulacement  in  the  relative  levels  of  the  sea  and  land. 


RELATIONS   OF  THE  SEA    TO    THE  LAND.       105 

Although  monotonous  in  aspect,  they  are  as  imposing 
monuments  of  past  work,  of  past  activity,  as  are  the 
peaks,  pinnacles,  and  castles  that  have  been  worn  out 
of  the  dry  land  by  the  atmospheric  waters.  The  first 
tendency  of  the  oceanic  waters  is  to  level  all  inequali- 
ties to  a  uniform  surface ;  the  first  tendency  of  the 
atmospheric  waters  is  to  break  up  all  regular  surfaces 
into  inequalities.  The  work  is  in  opposite  directions ; 
but  it  all  tends  to  a  single  direction  in  the  end,  the 
monotonously  uniform  plain,  —  peneplain  or  plain  of 
marine  denundation,  whichever  it  may  happen  to  be. 

The  Dismemberment  of  the  Land  by  the  Sea.  —  The 
rate  at  which  oceanic  destruction  takes  place  depends 
naturally  upon  a  number  of  distinct  conditions,  not  the 
least  important  of  which  is  the  constitution  of  the  rock- 
masses  that  are  being  acted  upon.  Soft  rock  goes  much 
faster  than  hard  rock,  and  loose  and  incoherent  mate- 
rials still  faster  than  soft  rock.  On  some  parts  of  the 
English  coast,  slices  of  land  have  been  taken  out  at 
the  rate  of  three  feet,  or  even  more,  in  a  single  day; 
and  in  comparatively  short  periods  the  very  sites  of 
towns  and  villages  have  been  completely  lost  to  the 
sea.  Peninsulas  are  converted  into  islands,  islands 
are  cut  in  twain,  and  the  fragments  further  parcelled 
out  into  solitary  rocks  and  rocklets.  The  Hebrides, 
Shetlands,  Orkneys,  are  all  parts  of  what  at  one  time 
was  the  mainland  of  Britain,  just  as  Great  Britain  and 
Ireland  are  in  themselves  only  dismembered  parts  of  a 
formerly  united  Europe.  The  rocks  and  islands  off  our 
northern  New  England  coast  record  the  same  story,  as 
do  the  ocean-bound  cliffs  and  ledges  of  Nova  Scotia, 
Newfoundland,  and  Labrador.  (Plate  21,  Fig.  1.) 


106  THE  EARTH  AND  ITS   STOEY. 

It  is  not  always  easy  or  practicable  to  determine  just 
what  loss  an  extensive  land-mass  suffers  through  such 
oceanic  destruction :  some  parts  unmistakably  suffer  in 
the  complete,  or  almost  complete,  loss  of  their  material ; 
but,  again,  others  gain  through  the  wash  of  this  material 
to  them.  Despite  the  terrific  destruction  that  is  taking 
place  in  many  parts  of  the  British  coast,  it  seems  doubt- 
ful if  the  areal  surface,  taken  in  its  entirety,  has  lost 
anything  in  a  period  of  nearly  2,000  years.  The  wash 
of  one  part  has  accumulated  in  another,  and  thus  a  cer- 
tain measure  of  compensation  has  been  meted  out.  No 
one  who  has  not  seen  the  ocean  in  its  full  fury,  nor  any 
one  who  knows  it  only  in  regions  of  flat  sea-beaches, 
can  conceive  of  the  energy  that  is  put  into  the  destroy- 
ing power  of  its  waves.  These  in  themselves  rarely 
rise  higher  than  thirty-five  or  forty  feet;  but  where 
they  meet  the  vertical  cliffs  their  waters  are  frequently 
hurled  five  times  higher,  and  they  are  known  to  have 
been  tossed  to  three  hundred  feet,  and  to  do  execution 
even  at  that  height.  Blocks  of  rock  weighing  from  ten 
to  twenty  tons  have  been  washed  together  by  the  angry 
waters  at  elevations  of  fifty  or  sixty  feet  above  the 
sea ;  and  it  is  claimed  that  a  mass  of  concrete  weighing 
one  hundred  and  twenty-five  tons  was  moved  three  feet 
over  its  bed  in  the  harbor  of  Cette,  France.  Down- 
wards into  the  sea  itself  the  work  continues,  churning 
up  the  bottom  to  a  hundred,  two  hundred,  or  perhaps 
even  three  hundred  feet.  And  yet,  with  all  this,  the 
destruction  worked  by  the  ocean  probably  falls  far  be- 
low that  which  has  been  brought  about  by  the  atmos- 
pheric waters  and  the  running  waters  of  the  land. 

The   Ocean  as   a  Receiving  Basin.  —  A   short   time 


RELATIONS   OF  THE  SEA    TO    THE  LAND.       107 

ago  I  stood  upon  the  great  bridge  that  spans  the  Mis- 
sissippi River  at  St.  Louis,  and  looked  down  upon  the 
"  Father  of  Waters  "  slowly  rolling  its  course  to  the  open 
sea.  The  water  was  at  a  low  stage ;  and  on  either  side 
stood  out  dreary  expanses  of  mud-flats,  a  portion  of  the 
flood-plain  of  the  river.  For  miles  before  approaching 
the  stream  on  the  Illinois  side  we  travel  over  similar 
flat  reaches  of  ancient  flood-plain,  with  the  boundary 
hills  well  within  the  country.  Apart  from  the  fact 
that  it  was  the  Mississippi  River,  and  that  the  mud 
it  carried  away  with  itself  was  a  part  of  American  soil, 
there  was  nothing  specially  attractive  about  the  picture  ; 
and  probably  it  was  not  nearly  so  inspiring  as  some 
would  have  wished.  But  it  awakened  within  me  the 
reflection :  What  does  it  all  mean  ? 

Ages  ago,  where  the  stream  is  now  flowing,  there 
was  ocean,  the  same  ocean  to  which  the  river  is  to-day 
pressing  forward  its  mud  sediment.  The  configuration 
of  the  rocks  declares  it  to  have  been  so ;  the  landscape 
shows  it.  At  that  time  the  American  continent  was 
perhaps  divided  into  two  halves,  with  the  waters  of  the 
Gulf  of  Mexico  extending  far  into  British  America, 
and  to  the  very  base  of  the  western  mountains.  Let 
any  one  visit  the  delightful  Colorado  Springs,  and  look 
south  along  the  line  of  the  Rockies,  and  it  will  not 
take  him  long  to  recognize,  in  the  gently  sloping  coun- 
try that  rolls  off  eastward  in  the  direction  of  the  Mis- 
sissippi, the  ancient  floor  of  the  sea,  —  much  of  it  still  as 
perfect  as  if  it  had  been  laid  dry  only  yesterday.  Grad- 
ually the  land  lifted,  the  waters  were  called  off,  and 
the  country  was  united  into  a  single  whole.  Over  this 
ancient  floor  of  the  ocean  now  flows  the  Mississippi. 


108  THE  EARTH  AND  ITS   STORY. 

The  Sediment  Discharge  of  Rivers.  —  If  we  take  a 
certain  quantity  of  this  St.  Louis  water  and  weigh  it, 
together  with  an  equal  quantity  of  pure  water,  we  shall 
have  no  difficulty  in  ascertaining  just  what  proportion 
of  impurity  is  held  in  suspension  by  the  water,  —  in 
other  words,  how  much  mud  is  distributed  through 
every  gallon-measure  of  the  river.  And  if  over  a 
given  line  we  can  calculate  how  many  gallons  of  water 
are  being  passed  by  the  river  in  any  definite  period  of 
time,  whether  week,  month,  or  year,  it  becomes  an 
easy  computation,  by  the  simple  rule  of  multiplication, 
to  tell  just  how  much  sediment  is  being  swept  along  in 
the  same  space  of  time.  With  a  point  of  observation 
placed  nearer  to  the  mouth  of  the  river,  or  below  its 
last  tributary,  we  should  by  the  same  process  be  in  a 
position  to  estimate  the  total  amount  of  sediment  that 
was  being  gathered  in  from  the  entire  Mississippi  basin, 
inasmuch  as  the  main  stream  and  its  tributaries  are  the 
arteries  of  drainage  for  that  basin.  This  has  been 
done,  and  it  is  shown  that  the  river  actually  discharges 
every  year  not  less  than  7,500,000,000  cubic-  feet  of 
solid  mud  material. 

What  is  the  significance  of  this  enormous  discharge  ? 
It  means  simply  that  this  amount  of  material,  if  spread 
out  and  evenly  distributed  over  the  floor  of  the  Missis- 
sippi basin,  would  elevate  that  floor  (making  the  neces- 
sary allowance  for  compacting  into  rock),  by  J0  of  a 
foot  in  a  century,  or  by  one  foot  in  six  thousand  years. 
To  state  the  proposition  in  a  reversed  way,  the  river 
with  its  tributaries  removes  from  all  parts  of  its  drain- 
age basin,  on  an  average,  one  foot  of  solid  material  in 
every  six  thousand  years.  Now,  if  we  assume  that  all 


RELATIONS   OF  THE   SEA    TO    THE  LAND.       1Q9 

the  rivers  of  the  continent  are  doing  an  equivalent 
amount  of  work  in  their  own  drainage  basins,  then 
must  the  entire  continent  be  losing  material  to  an 
amount  equal  to  a  uniform  surface  of  one  foot  in  thick- 
ness, covering  its  entire  expanse.  By  several  methods 
of  calculation  it  has  been  determined  that  the  average 
elevation  of  the  continent,  with  its  mountains,  plains, 
and  hollows,  is  approximately  1,200  feet ;  therefore, 
were  there  no  counteracting  influences,  the  whole  sur- 
face would,  by  the  method  of  denudation  that  has 
here  been  outlined,  be  washed  down  to  the  sea-level 
in  a  little  over  7,000,000  years.  In  reality,  the  time 
would  not  be  so  long;  as  the  amount  of  destruction 
that  has  been  calculated  does  not  include  the  materials 
that  are  removed  invisibly  through  chemical  solution, 
and  which  probably  amount  to  a  full  twenty  per  cent  of 
the  materials  carried  out  in  mechanical  suspension. 

The  Making  of  New  Land.  —  We  ask  ourselves:  To 
what  end  does  all  this  material  go  ?  The  region  of  the 
mouth  of  the  river,  where  the  several  "  Passes "  are 
forging  their  way  into  the  Gulf,  gives  the  answer  to 
this  question.  It  is  there  that  the  river-mud  has 
already  accumulated  to  a  depth  of  700  feet  and  more, 
and  from  there  it  is  transported  by  various  currents 
to  different  parts  of  the  continental  border.  The 
Ganges  is  doing  much  the  same  for  India,  the  Nile  for 
Africa,  the  Amazons  for  South  America,  the  Rhine,  the 
Rhone,  the  Po,  etc.,  for  Europe.  Behind  deltas,  in 
front  of  deltas  ;  in  estuaries,  out  of  estuaries,  —  the  sea 
is  being  filled  in.  Islands,  bars,  sand-strips,  and  lagoon- 
barriers  are  being  formed;  and  between  them  and  the 
main  coast  new  strips  of  territory  are  created.  In 


110  THE  EARTH  AND  ITS   STORY. 

this  way  the  continents  grow  and  expand,  only  to  be 
worn  down  and  destroyed  elsewhere.  Ravenna,  which 
during  the  Roman  period  was  situated  on  the  shores 
of  the  Adriatic,  is  now  removed  through  the  outward 
growth  of  the  Italian  peninsula  four  miles  from  the 
sea;  Ostia,  the  former  port  of  Rome,  is  to-day  an 
inland  city,  with  a  land-strip  of  three  miles  separating 
it  from  the  Mediterranean.  And  the  fate  of  these  two 
cities  threatens  Venice,  looking  towards  a  future  not 
very  distant. 

Many  of  the  finest  alluvial  lands  of  the  world  are  the 
joint  product  of  river  down-wash  and  oceanic  recon- 
struction. The  fertile  plains  of  Lombardy,  Piedmont, 
and  Venetia  represent  in  the  main  a  former  bight  of 
the  Adriatic,  which  has  been  filled  in  by  the  debris 
that  has  been  washed  off  from  the  southern  face  of  the 
Alps ;  the  great  jungle  plains  of  Northern  India,  which 
run  up  to  and  skirt  the  base  of  the  Himalaya  chain, 
are  in  the  same  way  only  an  infilling,  with  the  materials 
derived  from  those  mountains,  of  a  portion  of  the 
former  Indian  Ocean.  The  peninsula  of  India  is  to-day 
a  part  of  the  Asiatic  continent,  but  in  past  periods  its 
heart  was  distinct  and  far  from  the  northern  land-mass. 
The  ocean  is  thus  the  great  accumulator  of  sediments, 
and  the  source  which  furnishes  the  new  materials  for 
the  building  up  of  the  continents.  In  it  .the  new  rocks 
are  formed,  and  not  only  from  the  loose  sediments  of 
mud,  sand,  and  pebble,  but  from  the  invisible  lime 
which  is  carried  out  in  solution  by  the  terrestrial 
waters,  and  in  the  ocean  separated  by  vital  agencies 
into  the  hard  parts  of  shell,  coral,  etc. 


THE  EARTH  IN  ITS  INTERIOR.  Ill 


CHAPTER   IX. 

THE    EARTH   IN   ITS    INTERIOR. 

THE  text-books  of  a  quarter  of  a  century  ago,  and 
some  of  them  even  to-day,  tell  us  that  the  earth  is  a 
hollow  shell,  filled  nearly  to  the  surface  with  fiery 
molten  material.  The  hard  crust,  so-called,  was  fre- 
quently assumed  to  be  not  more  than  forty  or  fifty 
miles  in  thickness,  and  sometimes  even  less.  The 
reasons  that  were  given  in  support  of  this  conclusion 
can  be  summed  up  in  a  few  words :  Volcanoes  throw 
out  molten  material  from  the  interior ;  a  steadily  in- 
creased heat  is  known  to  follow  every  descent  into  the 
earth's  interior ;  the  crust  shows  prodigious  movements, 
which  can  only  be  explained  on  the  assumption  that 
the  mass  is  freely  suspended  or  floated.  The  objec- 
tions that  if  the  earth  were  this  thin  shell  it  would 
yield  to  the  same  kind  of  deformation  which  is  im- 
posed upon  the  oceanic  waters  through  solar  and  lunar 
attraction;  and  that  the  inner  fluid  material  might  in 
itself  make  "  tides,"  and  from  time  to  time  disrupt  its 
enclosing  walls,  —  were  not  considered,  certainly  not  in 
their  proper  significance.  The  researches  of  to-day 
show  almost  conclusively,  and  to  most  physicists  per- 
haps conclusively,  that  the  planet  is  virtually  solid  to 
the  core,  and  that  it  bears  itself  with  the  rigidity  of 
steel  or  glass.  This  conception,  which  is  so  fundamen- 


112  THE  EARTH  AND  ITS   STORY. 

tally  opposed  to  former  notions,  is  based  primarily  upon 
a  rigid  mathematical  determination ;  and  there  are  no 
facts  in  geology  that  are  opposed  to  it. 

The  Internal  Heat.  —  Every  one  who  has  descended 
into  a  deep  mine,  where  the  cold  outside  air  has  not 
been  introduced  by  blowing  fans,  knows  how  much 
warmer  it  is  below  than  above ;  if  the  mine  is  very 
deep,  the  heat  is  all  but  unbearable,  and  for  working 
purposes  practically  so.  At  3,000  feet,  or  a  little  more 
than  half  a  mile,  the  temperature  in  our  coal-mines 
would  be  uniformly  about  100°  F.,  at  5,000  feet 
nearly  150°.  Over  the  entire  earth,  barring  some 
specially  exceptional  spots,  there  seems  to  be  a  steady 
increase  of  temperature  of  approximately  1°  F.  for 
every  50  or.  60  feet  of  descent.  Occasionally  this 
amount  is  increased  to  about  1°  for  every  35  feet,  and 
about  as  often  reduced  to  1°  in  every  75  feet.  A  re- 
cent boring  in  the  Lake  Superior  region  gives,  very 
exceptionally,  an  increase  of  only  1°  for  about  200  feet. 
The  steady  increase  begins  at  that  point  beneath  the 
surface  which  marks  the  farthest  penetration  of  the 
heat-rays  of  summer  and  the  cold  of  winter,  —  in  other 
words,  where  there  is  an  equable  temperature  the  year 
round,  and  where  this  temperature  marks  the  annual 
average  for  the  locality  that  is  immediately  above  it. 
Such  a  spot  is  generally  found  at  a  depth  of  not  more 
than  60  or  80  feet  beneath  the  surface. 

With  a  steady  increase  beyond  this  point  of  1°  F.  for 
every  50  or  60  feet,  it  takes  no  very  great  depth  to  give 
a  prodigious  amount  of  heat.  At  10,000  feet  in  the 
latitude  of  New  York  or  Philadelphia,  the  temperature 
would  be  that  of  the  boiling-point  of  water.;  and  at 


THE  EARTH  IN  ITS  INTERIOR.  113 

thirty  miles,  3,000°,  or  about  sufficient  to  fuse,  at  the 
ordinary  melting-point,  the  most  refractory  substances 
known  to  us.  The  melting-point  of  gold  is  about 
2,500°  F. ;  of  platinum  about  3,200°.  It  is  the  recog- 
nition of  this  fact,  and  the  knowledge  that  very  much 
higher  temperatures  must  exist  still  farther  within  the 
interior,  which  gave  such  strong  support  to  the  notion 
of  internal  fluidity ;  for,  it  was  argued,  no  substance, 
unless  it  was  of  a  character  that  is  now  entirely  un- 
known to  us,  could  withstand  the  enormously  high 
temperature  of  the  deep  interior  without  either  liquefy- 
ing or  volatilizing.  The  condition  here  indicated  is  not, 
however,  borne  out  by  the  facts.  When  we  subject  a 
body  to  a  high  degree  of  pressure,  we  at  the  same  time 
materially  raise  its  "  melting-point,"  or  point  of  fusion. 
What  would  under  ordinary  conditions  melt  at  perhaps 
200°,  may  not  with  this  pressure  imposed  upon  it  melt 
at  less  than  250° ;  and  under  still  greater  pressure,  it 
may  only  melt  at  2,000°,  or  perhaps  not  at  all.  The 
earth's  mass  reacts  upon  itself  with  such  enormous 
pressure,  that  it  is  by  no  means  unlikely  that  the 
greater  number  of  substances  within  the  interior  do 
not  melt,  even  at  temperatures  of  4,000°  or  5,000°, 
simply  because  they  cannot  obtain  release.  This  is 
an  important  condition,  and  it  permits  us  to  harmonize 
the  behavior  of  the  different  substances  of  the  interior 
with  the  conception  and  mathematical  determination  of 
a  rigid  interior. 

It  has  not  yet  been  determined  what  is  the  greatest 
amount  of  heat  that  is  to  be  found  in  the  earth's  in- 
terior. It  has  been  shown  by  Sir  William  Thomson 
that  beyond  a  certain  depth,  of  perhaps  80  to  100 


114  THE  EAETH  AND  ITS  STOEY. 

miles,  the  increase  is  a  rapidly  diminishing  one,  and  it 
is  probably  not  straining  the  truth  when  it  is  assumed 
that  the  warmest  temperature  need  not  exceed  7,000° 
or  8,000°.  Many  people  believe  that  this  great  heat 
has  much  to  do  with  determining  climate,  giving  to 
the  surface  a  generous  distribution  of  warmth,  and  so 
forth ;  as  a  fact,  its  influence  is  not  felt  on  the  surface 
at  all,  not  even  to  the  extent  of  melting  in  the  course 
of  a  full  year  a  sheet  of  ice  of  a  millimeter  in  thickness 
and  covering  the  globe.  Nor  does  it  seem  to  have 
affected  the  climate  in  any  of  the  past  geological  periods, 
except,  possibly,  in  the  very  earliest. 

Pockets  of  Molten  Material.  —  It  is  not  natural  for 
all  persons  to  conceive  alike  of  this  condition  of  terres- 
trial solidity.  Those  who  live  in  the  neighborhood  of 
active  volcanoes  do  in  truth  see  molten  material  thrown 
out  from  the  "bowels  of  the  earth;  "  this  is  certainly 
evidence  of  internal  liquidity  of  some  kind.  There  are, 
however,  a  number  of  causes  that  can  work  toward 
liquefying  portions  of  the  interior  without  thereby  sen- 
sibly affecting  the  greater  mass.  We  do  not  say  that 
iron  is  not  solid  because  it  contains  a  number  of  air- 
bubbles  ;  nor  is  ice  liquid  when  its  mass  is  riddled 
with  air  and  water  holes.  In  the  same  way,  the  earth 
may  have,  and  doubtless  does  have,  pockets  of  liquid 
or  molten  material,  and  perhaps  even  a  complete  shell 
of  it,  underlying  the  surface  at  no  very  great  depth; 
and  yet  the  presence  of  such  "  filled  vacuities,"  being 
insignificant  in  area  as  compared  with  the  entire  mass, 
would  not  sensibly  disturb  the  argument  for  solidity. 
Of  the  ways  in  which  such  volcano-feeding  pockets 
may  arise,  it  is  only  necessary  to  enumerate  one  or  two. 


THE  EARTH  IN  ITS  INTERIOR.  115 

Proximity  to  a  field  of  special  chemical  activity,  where 
chemical  alterations  and  new  combinations  are  carried 
forward  with  particular  energy,  and  where  through 
such  processes  there  is  liberated  an  extra  quantity  of 
heat,  may  bring  about  local  liquefaction.  Again,  the 
same  result  may  follow  from  the  simple  operation  of 
removing  a  portion  of  the  pressure  that  keeps  down 
liquefaction,  —  a  sudden  lifting  off,  as  it  were,  of  a  por- 
tion of  the  melting-point,  —  whether  through  rock  dis- 
placements, the  absorption  of  rock  material  through 
chemical  solution,  or  otherwise.  And  probably  there 
are  many  local  spots  scattered  through  the  earth  where 
the  added  pressure  is  not  sufficient  to  overcome  the 
added  temperature,  and  where  consequently  the  rock 
appears  molten. 

An  abundant  proof  of  the  rising  temperature  within 
the  earth  is  -brought  to  us  by  the  numerous  thermal 
springs  which  issue  at  the  surface.  They  acquire  their 
special  temperatures  by  traversing  the  heated  regions 
below;  and  their  own  heat  is  the  index  of  the  depth 
to  which  they  penetrate,  or  whence  they  arise.  The 
greater  the  penetration,  the  more  highly  heated  will 
they  come  to  the  free  air;  some  of  this  acquired  heat 
is  lost  in  the  passage  of  the  spring- waters  to  the  sur- 
face, but  enough  is  retained  to  permit  of  a  fair  estimate 
of  the  depth  whence  the  water  has  risen.  In  some 
regions,  especially  in  the  vicinity  of  volcanoes,  a  high 
temperature  may  be  acquired  as  the  result  of  simple 
contact  with  chemically  heated  bodies,  and  entirely 
independent  of  the  matter  of  depth. 

The  Density  or  Weight  of  the  Earth.  —  There  is  no 
possibility  of  finding  out  to  what  extent  the  deeper 


116  THE   EARTH  AND   ITS   STORY. 

rocks  of  the  globe  differ  from,  or  agree  with,  those  that 
are  known  to  us  at  the  surface.  By  various  methods 
of  computation  it  has  been  determined  that  the  average 
weight  of  the  earth's  materials  is  about  5.5  times  that 
of  water,  and  about  double  that  of  the  superficial  rocks. 
This  being  the  case,  it  must  follow  that  much  of  the 
interior  has  a  density  at  least  7  or  10  times  that  of 
water,  and  not  impossibly  of  15  or  even  20  times.  It 
has  accordingly  been  urged  that  probably  the  deeper 
parts  are  largely  metallic  in  nature,  or  even  pure  metal. 
But  it  cannot  be  overlooked  that,  under  the  strain  of 
the  earth's  enormous  pressure,  even  the  ordinary  super- 
ficial rocks,  whether  granites,  sandstones,  or  limestones, 
might  be  so  well  compacted  as  to  have  their  normal 
hardness  far  exceed  that  which  belongs  to  average  rock. 
Yet  it  is  by  no  means  impossible,  or  even  unlikely,  that 
vast  metallic  deposits  do  occur  within  the  deep  interior. 


VOLCANOES,   AND    WHAT   THEY   TEACH.          117 


CHAPTER    X. 

VOLCANOES,  AND  'WHAT  THEY  TEACH. 

The  Aspects  of  a  Volcano;  Vesuvius.  —  Text-books  of 
geography  ordinarily  describe  the  volcano  as  a  moun- 
tain that  "  throws  out  lava,  fire,  and  smoke."  Were 
you  to  saunter  out  of  a  quiet  morning  along  the  shores 
of  the  Bay  of  Naples,  and  cast  your  eye  back  to  the 
landscape  which  bounds  the  ocean  to  the  east,  you 
would  observe,  rising  up  in  its  own  peculiarly  graceful 
form,  a  mountain  that  differs  essentially  from  the  ordi- 
nary mountains  to  which  we  have  become  accustomed. 
Vesuvius  rises  with  a  gentle  sweep  from  near  the  sea, 
its  slope  so  gradual  at.  first  as  hardly  to  give  it  the 
appearance  of  a  mountain.  Farther  OA,  the  steepness 
of  slope  rapidly  increases ;  and  for  about  the  last  1,500 
feet  of  vertical  height,  the  rise  is  so  rapid  that  the 
mountain  may  be  said  to  go  up  like  a  ucone."  At  the 
summit  we  have  reached  an  elevation  slightly  exceed- 
ing 4,000  feet.  Could  this  mountain  be  divested  of 
all  the  surroundings  that  do  not  properly  belong  to  it, 
it  would  present  much  the  same  appearance  from  all 
points  of  the  compass  as  it  does  from  the  ocean-side, 
—  a  characteristic  of  uniformity  that  belongs  to  nearly 
all  perfect  volcanoes.  When  I  visited  the  mountain  a 
few  years  ago,  the  top  was  occupied  by  a  great  depres- 
sion or  pit,  of  possibly  300  to  400  feet  diameter,  and 


118  THE  EARTH  AND  ITS   STORY 

80  or  100  feet  in  depth,  from  the  bottom  of  which 
issued  vast  curling  wreaths  of  heated  vapor,  and  more 
or  less  frequent  showers  of  red-hot,  and  nearly  white- 
hot,  rock-material,  —  "cinders,"  as  they  might  perhaps 
properly  be  called.  I  descended  into  this  great  depres- 
sion, or  crater  as  geologists  call  the  hollow,  and  cau- 
tiously approached  the  centre,  where  nearly  all  the 
active  work  was  going  on.  The  rock-floor  over  which 
my  steps  were  directed  was  glowing  in  places  with  red 
heat,  and  it  did  not  take  much  study  to  tell  me  that 
there  was  little  between  the  soles  of  my  boots  and  a 
seething,  fiery  mass  below.  It  was  a  thin  crust,  but 
sufficient  to  hold  me.  Somewhat  to  one  side  of  the 
centre  of  the  crater  there  was  a  diminutive  mound-like 
elevation  or  uconelet,"  hardly  more  than  four  or  five 
feet  in  elevation ;  and  from  it  was  issuing  all  that 
tumultuous  vapor  and  flying  rock  which  I  had  observed 
from  the  crater-rim.  (Plate  37.) 

The  Operations  of  a  Volcano.  —  From  my  position 
near  the  base  of  the  conelet  the  operations  of  the  moun- 
tain could  be  easily  followed.  A  great  explosion  of 
steam  would  sometimes  be  accompanied  by  a  liberal 
outpouring  of  red-hot  cinders,  and  less  often  by  an 
actual  outflow  of  the  molten  material  in  mass  —  the 
lava.  Frequently  the  liberation  of  steam  was  unat- 
tended by  outpouring  of  any  kind,  but  was  followed  by 
a  sound  like  rolling  thunder,  ending  with  a  "  thud,"  as 
though  something  massive  had  fallen  to  the  bottom. 
With  a  little  courage  added  to  my  desire  for  study, 
and  with  the  wind  blowing  well  over  my  back,  I  ran, 
at  favorable  moments,  to  the  top  of  the  conelet,  and 
looked  into  the  furnace  below.  Now  and  then, 


UNIVERSE 


Plate  37. 


VOLCANIC   PHENOMENA. 

1.  The  cone  of  Vesuvius,  with  lava-fields  at  its  base.    V.  A  parasitic  cone.    N.  A  lava- 

plug,  marking  the  site  of  a  former  channel  of  eruption.    C.   Scoriaceous  lava. 
R.   llopy  lava,  showing  lines  of  flow. 

2.  The  brink  of  the  Vesuvian  crater. 


Plate  38. 


VOLCANIC   PHENOMENA. 

1.  Cascade  in  the  lava-flow  from  Kilauea,  Sandwich  Islands,  in  1880-1881. 

2.  Termination  of  lava-flow  from  Mauna  Loa  in  1880-1881. 


VOLCANOES,   AND   WHAT   THEY   TEACH.         119 

through  the  dissipating  vapor,  the  glowing  material 
which  formed  cinders  and  lava  was  easily  distinguish- 
able, and  the  eye  could  follow  without  difficulty  its 
ascent  through  the  funnel  or  neck  of  the  volcano. 
When  the  pent-up  vapor  had  sufficient  force  within  it- 
self to  elevate  the  seething  lava,  it  would  throw  it  out; 
at  other  times  it  broke  through  the  confining  magma, 
and  allowed  it  to  fall  back  to  its  interior  home.  A 
repetition  of  these  performances  constituted  the  volcanic 
action  of  a  volcano.  There  was  no  smoke,  there  were 
no  flames.  At  the  present  time  the  large  crater  no 
longer  exists.  The  activity  of  the  little  cone  has  com- 
pletely filled  it  up  with  its  ejected  material ;  and  the 
volcano  is  fiat-topped,  with  its  working  conelet  perched 
on  this  summit. 

The  Characteristics  of  a  Volcano.  —  Vesuvius  is  the 
type  of  by  far  the  greater  number  of  volcanoes  of  the 
earth's  surface ;  they  may,  therefore,  be  described  as 
conical  mountains  which  are,  or  have  been,  active  in 
throwing  out  molten  material,  whether  in  fragments 
(cinders,  ashes)  or  flowing  streams  (lava),  from  the 
earth's  interior,  the  ejecting  process  being  usually  ac- 
companied by  the  liberation  of  vast  quantities  of  the 
heated  vapor  of  water  (steam).  Our  definition  differs 
from  the  ordinary  geographical  one  in  eliminating  the 
matter  of  smoke  and  fire ;  the  former  is  only  the  quietly 
curling  steam,  and  the  latter  the  reflection  of  the  heated 
mass  below  on  this  vapor,  and  on  the  clouds  of  ashes 
that  go  up  with  it.  No  volcano  has  yet  been  found 
that  truly  smokes,  as  the  combustion  is  not  of  such  a 
nature  as  to  produce  smoke ;  and  it  is  only  in  most 
exceptional  cases  that  flames  have  actually  been  seen 


120  THE  EAETH  AND  ITS   STORY. 

in  a  crater  or  issuing  from  it.  When  they  do  occur, 
as  for  example  among  the  volcanoes  of  the  Hawaiian 
Islands,  they  represent  the  combustion  of  hydrogen  gas. 

The  closer  examination  of  the  outside  of  a  volcanic 
mountain,  such  as  Vesuvius,  shows  it  to  be  a  more  or 
less  regular  agglomeration  of  the  materials  of  eruption. 
Extensive  lava-beds  radiate  from  the  central  parts ;  and 
between  them  are  heaped  great  quantities  of  thrown-out 
blocks  and  cinders  (scoriae),  alternating  perhaps  with 
great  thicknesses  of  extremely  fine  sand.  Were  we  to 
slice  the  volcano  from  top  to  bottom,  we  should  also 
find  the  same  structure  in  the  interior,  the  materials, 
possibly,  bedded  among  themselves  with  a  certain 
amount  of  regularity.  If  our  section  were  made 
through  Cotopaxi  instead  of  Vesuvius,  or  through  Etna, 
or  Stromboli,  we  should  still  find  the  same  structure, 
—  which  leads  to  the  interesting  conclusion  that  vol- 
canoes are  built  up  through  the  materials  which  they 
themselves  throw  out.  The  mountain  may  be  ten  feet 
high,  or  it  may  be  ten  thousand,  but  the  fundamental 
structure  is  the  same.  (Plate  37,  Fig.  1.) 

Dimensions  of  Volcanoes. —  The  most  striking  dif- 
ferences that  are  to  be  found  among  volcanoes  relate 
principally  to  size,  to  the  contours  of  their  slopes,  and  to 
the  class  of  materials  which  they  put  out.  The  most 
gigantic  active  volcanoes  of  to-day  are  those  of  the 
Equatorial  Andes,  where  several  measure  17,000  to 
19,000  feet  in  height.  The  passively  active  cones  of 
Popocatepetl  and  Orizaba,  in  Mexico,  are  respectively 
17,500  and  18,200  feet  in  elevation.  Demavend,  on 
the  borders  of  the  Caspian  Sea,  said  by  some  to  be  fully 
20,000  feet  in  height,  may  still  be  active;  and  the 


VOLCANOES,   AND    WHAT   THEY   TEACH.  121 

exceedingly  active  Mauna  Loa,  of  the  Sandwich  Islands 
group,  which  rises  13,700  feet  out  of  the  water,  may 
properly  be  considered  as  rising  from  the  full  depth  of 
the  ocean,  nearly  17,000  feet  lower;  it  is  there  that  its 
base  is  implanted.  The  size  of  the  individual  parts  of 
a  volcano  are  in  no  way  dependent  upon  the  actual 
size  of  the  mountain  itself.  Thus,  while  such  a  colos- 
sus as  Popocatepetl  has  a  crater  not  more  than  two- 
thirds  of  a  mile  across,  the  cup  of  Kilauea,  a  mountain 
of  Hawaii  barely  more  than  one-fourth  the  height  of 
Popocatepetl,  measures  nearly  three  miles  in  greatest 
diameter;  and  the  crater  of  the  moderately  elevated 
Aso-San,  one  of  the  very  numerous  Japanese  volcanoes, 
exceeds  these  dimensions  by  fully  three  times.  Again, 
the  rather  insignificant  Skaptar  Jokull,  of  Iceland,  has 
on  more  than  one  occasion  thrown  out  lava  fields  of 
from  thirty-five  to  fifty  miles  in  length;  whereas,  in 
the  case  of  many  much  larger  cones,  the  lava  outflows 
have  never  reached  twenty  miles,  or  in  fact,  half  this 
length.  (Plate  39.) 

Composite  Cinder  and  Ash  Cones.  —  So  far  as,  the 
materials  of  discharge  are  concerned,  there  is  a  vast 
difference  between  them.  In  the  case  of  the  volcanoes 
of  the  Sandwich  Islands  group,  the  material  of  the  lava 
is  so  fluid  or  "glassy,"  and  there  is  so  little  paroxysmal 
discharge  of  steam,  that  the  outflowing  sheets  take  long 
and  easy  courses,  and  thereby  give  a  gentle  and  open 
contour  to  the  mountain ;  the  gradient  for  much  of  its 
course  is  not  over  three  degrees,  and  hardly  in  any 
place  exceeds  fifteen  degrees.  (Plate  38.)  Elsewhere 
the  lava  has  a  much  firmer  consistency,  flows  heavily, 
and  solidifies  at  comparatively  steep  angles ;  the  slope 


VOLCANOES,   AND   WHAT   THEY   TEACH.          123 

the  main  mass  of  the  lava,  and  which  now  constitute 
the  so-called  cinders  or  scorice.  These  when,  through 
rubbing  or  further  powdering  they  have  been  reduced 
to  a  fine  powder,  constitute  volcanic  ash.  Pumice  is 
only  a  glassy  form,  in  exceedingly  light  weight,  of 
volcanic  cinder.  It  should  be  noted  here  that  the 
article  known  to  jewellers  as  lava  is  in  most  cases 
only  a  hardened  paste  or  cement  of  ash  and  water,  a 
puzzuolana  or  tuff.  The  material  which  covers  Pompeii 
is  largely  of  this  nature. 

The  Working  Activity  of  Volcanoes.  —  Sometimes  a 
single  eruption  marks  the  entire  history  of  a  volcano. 
More  generally  a  number  of  eruptions  follow  one  upon 
another,  the  intervals  of  quiescence  being  very  irregu- 
lar, ranging  from  a  few  months,  or  even  weeks,  to 
years  and  centuries.  It  is  often  difficult  to  tell  just 
when  a  volcano  is  "extinct,"  since  an  eruption  might 
at  any  time  suddenly  remove  the  dormancy  which  had 
been  supposed  to  mark  extinction.  There  are  a  few 
volcanoes,  such  as  Stromboli  in  the  Mediterranean, 
which  are  continuously  active.  Vesuvius  has  itself 
been  in  eruption  a  part  of  almost  every  year  for  the 
last  period  of  nearly  a  quarter  of  a  century;  but 
through  the  past  eighteen  hundred  years,  or  since  the 
great  eruption  of  A.D.  79,  which  overwhelmed  Pompeii 
and  Herculaneum,  there  have  been  long  intervals  of 
repose.  The  intensity  of  eruption  depends,  to  some 
extent,  upon  the  length  of  time  that  the  mountain  has 
remained  passive ;  or,  what  is  probably  nearer  to  the 
truth,  upon  the  firmness  with  which  its  parts  have  been 
sealed  and  "plugged"  up  during  the  period  of  repose. 
The  tightly  fitting  lava  that,  on  the  cessation  of  activ- 


124  THE  EARTH  AND  ITS   STORY. 

ity,  has  solidified  as  a  plug  in  the  neck  of  the  volcano, 
keeps  down  for  a  while  the  energy  that  is  boiling  below ; 
and  when  the  eruption  finally  comes,  if  it  comes  at  all, 
it  may  present  itself  in  a  true  paroxysm.  (Plate  40.) 

In  a  number  of  cases  it  is  believed  that  the  whole 
top  of  a  cone  has  been  blown  out  by  a  sudden  explo- 
sion of  this  }dnd;  the  mountain  is  said  to  have  been 
"gutted."  In  the  great  eruption  which  took  place  in 
the  Sunda  Sea  in  August,  1883,  the  small  island  of 
Krakatao,  lying  off  Java,  was  literally  shattered  to 
pieces,  and  almost  all  of  it  disappeared  beneath  the 
water;  only  fragments  indicated  the  former  position 
of  the  crater.  Even  in  the  case  of  Vesuvius,  it  is 
frequently  assumed  that  the  eruption  of  A.D.  79  blew 
off  the  top  of  the  volcano  which  produced  the  mis- 
chief: it  is  certain  that  the  Vesuvius  of  to-day  is  not 
that  mountain,  even  if  it  stands  on  nearly  the  same 
spot;  for  surrounding  it,  in  massive  rock- walls,  are  the 
fragments  of  its  ancient  predecessor,  quiet  with  the 
repose  of  the  centuries.  Locally  these  parts  of  the  old 
crater  wall  (crater-ring)  are  known  as  Monte  Somma. 
After  the  long  interval  that  has  followed  an  eruption 
of  this  kind,  it  is  not  easy  to  ascertain  the  precise  order 
of  events  as  they  presented  themselves,  and  some 
geologists  hold  as  questionable  the  opinion  which 
ascribes  decapitation  to  the  mountain;  they  prefer  to 
believe  in  the  collapse  or  "  inf ailing  "  of  the  top  of  the 
volcano,  and  there  is  no  question  that  this  condition 
often  follows  a  violent  explosion.  The  eruption  loosens 
the  interior,  and  paves  the  way  for  a  subsidence. 

Shifting  of  the  Points  of  Activity ;  Parasitic  Cones. 
A  long  period  of  dormancy  in  a  volcano  frequently 


Plate  42. 


VOLCANIC  PHENOMENA. 
1.  The  trap-dike  of  West  Conshohocken,  Pa.,  where  the  hard  and  resisting  rock  cuts 

through  the  hydro-mica  schist. 
2-  The  "  steps  "  and  columns  of  basalt  of  the  Giant's  Causeway,  Ireland. 


VOLCANOES,   AND   WHAT   THEY  TEACH.        125 

leads  to  the  breaking  through  in  a  new  place  of  the 
next  eruption ;  geologists  speak  of  the  "  travelling  "  of 
the  seats  of  activity.  In  Etna,  for  example,  the  active 
points  have  shifted  numerously  since  the  beginning  of 
the  Christian  era.  In  addition  to  the  main  central 
opening,  the  mountain  is  provided  with  a  large  number 
of  secondary  openings,  set  in  little  monticules  of  their 
own,  the  so-called  parasitic  cones.  These  afford  re- 
lease from  the  strains  of  the  interior  in  the  same  way 
that  the  principal  opening  does,  and  through  them  large 
quanties  of  lava  and  ashes  are  thrown  out.  The  erup- 
tion of  1886  from  the  Monte  Gemmellaro,  a  parasitic 
cone  on  Etna,  sent  out  a  lava  stream  the  dimensions  of 
which  were  estimated  at  sixty-six  million  cubic  metres. 
Whether  or  not  these  accessory  cones  are  fed  from  a 
main  single  channel  of  lava  running  up  approximately 
to  the  centre  of  the  volcano,  or  from  independent 
isources  of  their  own,  can  only  be  determined  from  a 
dissection  of  the  mountain.  But  whether  one  way  or 
another,  the  masses  of  lava  that  have  hardened  solid 
in  all  the  passages  stand  like  the  branches  of  a  tree, 
penetrating  the  mountain  in  all  directions.  They  are 
the  volcanic  "dikes"  of  geologists.  (Plate  37,  Fig.  1.) 
The  After-History  of  a  Volcano.  —  The  volcano  may 
have  served  its  time ;  life  has  left  it,  and  it  begins  to 
decay  and  crumble.  In  place  of  the  boiling  crater, 
which,  if  not  always  active,  was  at  least  always  threat- 
ening with  possibilities  of  activity,  we  have  a  peaceful 
hollow,  now  perhaps  put  to  the  humble  but  useful 
labors  of  man.  The  swarthy  Mexican  Indian  may  fre- 
quently be  seen  furrowing  with  his  rude  ploughshare 
the  soil  that  once  quaked  and  trembled  with  the  ener- 


126  THE  EARTH  AND  ITS   STORY. 

gies  that  were  stored  up  beneath  it.  The  crater  was 
his  field  —  a  smiling  garden  of  aloe  or  sugar-cane. 
The  beautiful  lakes  of  Central  and  Southern  Italy  — 
Albano,  Nemi,  Bolsena,  Bracciano,  Avernus,  Fusaro  — 
are  the  eyes  of  ancient  craters,  reflecting  to-day,  not 
the  fire  of  the  interior,  but  the  quiet  of  the  Mediter- 
ranean sky.  The  Balaton  of  Hungary  is  another  of 
these  crater-lakes,  as  is  also  the  not  inappropriately 
named  Crater  Lake  of  Oregon.  High  up  in  the  Ne- 
vado  de  Toluca,  of  the  Mexican  plateau,  fourteen  thou- 
sand feet  high,  is  one  of  these  "  eyes  of  the  sea,"  one 
of  the  loftiest  of  all  known  lakes.  All  these  beauties 
of  nature  are,  however,  doomed  to  destruction. 

The  mountain  continues  to  wear ;  its  slopes  are  fur- 
rowed by  running  and  tumbling  brooks  and  cascades  ; 
the  very  core  is  reached ;  and  for  a  time  perhaps  noth- 
ing stands  but  the  great  central  plug  of  lava  —  the 
neck  or  chimney  —  around  which  the  energies  of  the 
volcano  were  centred.  (Plate  44.)  It  stands  grimly 
out  of  the  landscape,  reading  for  it  a  history  that  is  not 
less  interesting  than  it  is  ancient.  It  is  not  a  matter  of 
a  few  years  over  which  this  destruction  has  taken  place, 
but  of  centuries  and  of  tens  of  centuries.  Further 
yet  the  destruction  continues,  until,  possibly,  time  has 
le veiled  all,  and  effaced  the  history.  We  then  search 
for  the  record  in  the  rock-masses  about,  and  perhaps 
find  vast  heaps  and  deposits  of  volcanic  ash  and  cin- 
ders, of  giant  lava  beds,  scattering  over  the  country. 
They  may  live  long  after  the  mountain  which  gave 
them  birth  has  itself  disappeared ;  but  in  course  of  time 
they,  too,  will  go.  Far  and  wide  over  the  earth's  sur- 
face we  meet  with  the  evidences  of  vulcanism,  of 


Plate  44. 


VOLCANIC   PHENOMENA. 

Mato  Tepee,"  or  "  Bear  Lodge,"  Wyoming,  a  basaltic  tower,  625  feet  in  height,  the 
remains  of  an  ancient  lava  injection  which  was  forced  upward  through  sedi- 
mentary strata,  now  removed  by  erosion. 


VOLCANOES,    AND   WHAT   THEY   TEACH.        127 

volcanic  energy  that  has  spent  itself  ages  ago,  or  of 
such  as  has  only  recently  passed  to  slumber.  Probably 
at  no  time  in  the  history  of  our  planet  since  the  first 
rock  was  formed  has  there  been  an  absence  of  vol- 
canic action ;  and  unmistakably  during  certain  periods 
of  this  history  the  activity  was  much  more  pronounced 
than  it  is  to-day. 

The  Causes  of  Eruption.  —  This  is  as  yet  an  unsolved 
problem.  The  presence  of  water  at  the  seat  of  vol- 
canic action,  and  the  conversion  of  water  into  its  ex- 
pansive and  explosive  form  of  steam,  have  generally 
been  considered  to  be  the  conditions  that  bring  about 
eruption,  and  without  which  it  has  been  assumed  there 
could  not  be  much  of  it.  Many  difficulties  connect 
themselves  with  this  explanation,  not  the  least  among 
which  is  the  fixed  positions  which  the  volcanoes  oc- 
cupy, and  the  fact  that, water  could  only  be  an  activo 
agent  in  the  work  when  the  material  for  this  work 
had  already  been  prepared  for  it.  While,  thereforev 
water  and  the  vapor  of  water  are  unquestionably  asso- 
ciated with  volcanic  phenomena,  and  may  even  be 
directly  instrumental  in  bringing  about  certain  of  their 
phases,  it  seems  more  in  accordance  with  the  succession 
of  events  to  consider  them  as  secondary  rather  than  as 
primary  causes.  It  is  by  no  means  unlikely  that  much 
of  the  pushing  and  upheaving  of  lava  is  due  to  con- 
tractional  impulses  of  the  great  mass  of  the  crust  —  a 
squeezing-up,  as  it  were,  of  the  fluid  matter  of  the 
interior  at  points  where  this  fluid  material  is  most 
abundant,  and  where  the  strain  of  compression  can  be 
least  resisted.  Such  areas,  or  points  of  least  resistance, 
—  areas  of  weakness  they  might  be  termed,  —  we  have 


128  THE  EARTH  AND  ITS  STORY. 

a  right  to  search  for  along  the  troughs  of  the  different 
oceans,  and  on  the  border-land  of  the  continents  and 
oceans.  It  is  in  truth  in  such  regions  that  we  find 
almost  the  entire  force  of  volcanic  activity  to  have 
concentrated  itself. 

Fissure  Eruptions.  —  As  bearing  upon  the  possible 
or  probable  squeezing  up  of  the  molten  material  of  the 
interior  through  crustal  contraction,  instances  may  be 
cited  where  vast  quantities  of  lava  or  basalt  are  known 
to  have  appeared  at  the  surface,  not  in  isolated  crateral 
patches,  but  in  long  lines  of  fracture  or  fissure,  and 
without  the  accompaniment  of  those  fragmental  dis- 
charges which  are  associated  with  eruptions  of  the 
ordinary  kind.  These  fissure  eruptions  have  at  times 
been  continuous  over  lengths  of  fifty  and  a  hundred 
miles,  or  even  more,  the  lines  of  breach  being  often  as 
regularly  direct  as  though  they  had  been  artificially 
cut.  In  some  cases  the  fissures  are  only  a  few  feet  in 
width,  at  other  times  they  broaden  out  to  respectable 
dimensions;  but  in  one  way  or  another  they  have 
thrown  out  an  enormous  amount  of  material.  In  the 
Northwestern  United  States  —  in  Oregon,  Washington, 
Idaho,  etc.  —  and  in  India  there  are  hundreds  of  thou- 
sands of  square  miles  covered  by  the  overflowing  sheets 
of  lava  issuing  from  such  fissures  ;  minor  fields  are 
found  in  various  parts  of  Gfreat  Britain,  in  Ireland,  in 
France,  etc.  In  the  Eastern  United  States  a  number 
of  long,  low  ridges  —  such,  for  example,  as  the  Orange 
Mountains  of  New  Jersey,  the  nobly  picturesque  Pali- 
sades of  the  Hudson  River  —  are  merely  erupted  masses 
that  stand  over  the  fissures  through  which  they  were 
extruded,  and  from  which  they  have  gently  flowed  off 


VOLCANOES,  AND   WHAT   THEY  TEACH.          129 

to  one  or  both  sides.  The  less  resisting  rocks  through 
which  they  forced  their  way  to  the  surface  having  worn 
more  rapidly,  they  now  stand  out  from  them  as  promi- 
nent walls  or  buttresses,  the  dikes  of  geologists.  It  is 
customary  to  give  to  the  ancient  fissure-rocks  the  name 
of  "trap,"  meaning  step,  from  the  circumstance  that 
the  rock  most  generally  presents  itself  in  step-like 
masses.  Columnar  structure  is  ordinarily  a  distinctive 
feature  of  trap,  which  includes  among  its  varieties  the 
basalt  of  the  Giant's  Causeway  and  Fingal's  Cave,  to 
which  reference  has  already  been  made.  (Plates  42,  43.) 
Laccolites.  —  It  has  not  yet  been  ascertained  in  what 
manner  the  fissures  giving  exit  to  this  vast  amount  of 
lava  were  formed.  In  many  cases,  probably,  they 
opened  as  the  result  of  straining  pressure  from  the 
interior  lava  itself ;  at  other  times  it  would  seem  that 
there  was  a  gentle  parting  of  the  earth's  crust,  and  that 
through  this  parting  (or  fissure)  lava  quietly  welled 
out,  and  then  overflowed  in  running  sheets.  It  looks 
as  if  the  Palisades  of  the  Hudson  River  may  have  been 
formed  in  this  quiet  way.  There  are,  however,  un- 
questioned cases  where  the  interior  lava  has,  under  the 
influence  of  crustal  pressure,  found  relief  in  raising  or 
"  doming  "  up  the  rock-masses  that  lie  above  it.  In 
this  way  it  reare  a  mountain,  and  without  showing  itself 
at  the  surface.  Thousands  of  feet  (in  thickness)  of 
rock-strata  have  been  made  to  yield  before  this  irresis- 
tible strain,  a  feature  in  the  landscape  most  beautifully 
shown  in  the  La  Sal  and  Henry  Mountains  of  Utah. 
Upheaved  mountains  of  this  Idnd  are  known  as  lacco- 
lites. 


130  THE  EARTH  AND  ITS   STORY. 


CHAPTER   XI. 

DISTRIBUTION    OF    VOLCANOES    AND    EARTHQUAKES. 

Distribution  of  Active  Volcanoes.  -  -  The  most  cursory 
examination  of  any  map  on  which  the  volcanoes  of  the 
world  are  plotted  shows  their  distribution  to  be  in  close 
correspondence  with  the  position  of  the  ocean.  There 
is  hardly  a  volcano  to-day  which  is  removed  two  hun- 
dred miles  from  it,  and  there  are  very  few  that  are  at 
as  great  a  distance.  A  belt  closely  circumscribes  the 
Pacific  basin,  following  the  Andean  and  Cordilleran 
chains  of  South  and  North  America,  and  connecting 
through  the  Aleutian  Islands  with  the  volcanoes  of 
Kamchatka,  and  with  those  of  the  disrupted  islands 
which  lie  east  and  south-east  of  the  continent  of  Asia 
—  Japan,  Philippines,  Sunda  Islands,  etc.  The  most 
destructive  centre  of  vulcanism  to-day  is  the  region  of 
the  Sunda  Sea,  following  from  Sumatra  and  Java  to 
Celebes  and  the  islands  beyond.  The  Asiatic  volcanoes 
alone  number  several  hundred ;  but,  with  the  exception 
of  those  on  the  peninsula  of  Kamchatka,  there  are  few 
that  are  located  on  the  continent  itself.  The  best 
known  of  these  are  Ararat  and  Demavend.  The  Cen- 
tral Pacific  has  the  great  volcanoes  of  the  Hawaiian 
Islands,  besides  less  important  ones  among  the  many 
islands  that  dot  the  region  of  Polynesia.  The  course 
of  the  Pacific  belt  is  continued  through  New  Guinea 


DISTRIBUTION   OF  VOLCANOES.  131 

and  New  Zealand,  with  a  possible  termination  in  Mount 
Erebus,  on  Victoria  Land  in  the  Antarctic  regions, 
beyond  the  78th  parallel  of  south  latitude. 

The  volcanoes  of  the  Atlantic  basin  are  mainly  in- 
sular, and  include,  among  others,  Hecla  and  Skaptar 
Jokull  on  Iceland,  the  volcano  of  Jan  Mayen,  Pico 
in  the  Azores,  the  Pic  de  Teyde  of  Teneriffe,  Strom- 
boli,  Etna,  and  Vesuvius  ;  the  last-named  is  the  only 
active  volcano  which  is  to-day  found  on  the  actual  con- 
tinent of  Europe.  Kilimanjaro,  Kenia,  and  the  Peaks 
of  Cameroon,  are  dormant  cones  of  Africa,  Mfumbiro 
and  the  cones  about  Lake  Rudolph  being  the  only 
active  or  half-active  volcanoes  of  that  continent. 

Seemingly  the  loftiest  of  all  known  volcanic  moun- 
tains, whether  active  or  extinct,  is  Aconcagua,  in  the 
Argentine  Republic,  approximately  23,000  feet  in  alti- 
tude. Bahama,  the  Nevado  de  Sorata,  Illimani,  and 
Chimborazo,  other  Andean  summits,  closely  rival  it; 
while  Cotopaxi,  with  an  altitude  of  nearly  19,000  feet, 
gives  to  us  the  picture  of  greatest  activity  combined 
with  lofty  elevation.  Mount  St.  Elias,  in  Alaska, 
which  was  formerly  supposed  to  be  a  volcano,  has  been, 
shown  by  recent  researches  not  to  be  volcanic.  Popo- 
catepetl, Orizaba  (or  Citlaltepetl),  and  Jorullo  are  semi- 
quiescent  volcanoes  of  the  Mexican  Republic ;  Colima 
and  Choboruco,  active  ones.  Within  the  domain  of  the 
United  States  there  does  not  appear  to  be  any  fully 
active  volcano  to-day,  but  extinct  or  quiescent  cones 
are  represented  in  Shasta,  Tacoma,  Hood,  and  Baker 
(the  last  active  as  late  as  1880?).  Besides  the  vol- 
canoes that  are  visible,  or  have  actually  come  to  light 
on  the  land-surface,  there  are  doubtless  hundreds  of 


132  THE  EARTH  AND  ITS   STORY. 

others  that  are  buried  in  the  sea,  and  that  manifest 
their  energies  unseen  to  the  world,  except  in  so  far  as 
the  products  of  eruption  are  cast  to  the  surface.  Much 
of  the  pumice  that  is  floating  about  on  the  free  surface 
of  the  ocean  is  undoubtedly  the  output  of  subaqueous 
volcanoes. 

Earthquakes.  —  Earthquakes  are  generally  associated 
with  volcanic  manifestations,  and  to  an  extent  they 
represent  identical  phenomena.  In  a  broad  character- 
ization they  are  merely  tremors  of  the  earth's  crust, 
the  movement  that  is  due  to  a  series  of  elastic  pulsa- 
tions or  waves  passing  through  it.  A  wagon  passing 
over  a  roadway  produces  a  slight  earthquake,  other 
causes  produce  larger  ones,  and  there  is  probably  no 
spot  on  the  earth  where  earthquakes  or  earth-tremors 
of  one  kind  or  another  do  not  take  place.  Manifestly 
where,  as  in  volcanic  regions,  great  disturbances  in  the 
rock-masses  are  the  order  of  occurrence,  it  would  be 
difficult  to  escape  the  making  of  earthquakes  ;  for  every 
dislocation,  every  break,  must  be  the  cause  of  some 
kind  of  jar.  It  is  this  frequent  interdependence  which 
has  united  in  the  popular  mind  the  two  types  of  phe- 
nomena. 

It  is  not  easy,  and  in  most  cases  perhaps  impossible, 
to  assign  a  cause  for  any  particular  earthquake,  espe- 
cially if  its  occurrence  is  in  a  non-volcanic  region.  In 
some  cases  it  may  have  been  the  result  of  a  simple  slip 
of  rock  at  the  surface,  in  the  not  very  extensive  manner 
of  the  ordinary  land-slide  ;  elsewhere  this  slip  may 
have  been  the  grandly  imposing  one  (not  necessarily 
visible  to  the  eye,  but  imposing  in  its  effects)  of  entire 
rock-masses,  of  different  degrees  of  construction,  slid- 


EARTHQUAKE  PHENOMENA.         133 

ing  away  from  one  another.  Some  of  the  earthquakes 
of  the  Atlantic  border  of  the  Eastern  United  States 
have  been  attributed  by  geologists,  whether  rightly  or 
wrongly,  to  the  slip  of  the  loose  materials  of  the  coastal 
plain  from  the  more  compact  granites  beyond.  The 
splitting  of  rocks  within  the  interior  must  be  a  fruitful 
source  of  earthquakes ;  and  perhaps  we  are  justified  in 
concluding  that  many  of  the  most  destructive  earth- 
quakes—  such  as  those  of  Lisbon  in  1755,  of  Caracas 
in  1812,  of  Ischia  in  1883,  and  of  Charleston,  S.  C., 
in  1886 — were  due  to  this  cause.  All  the  rocks  of 
the  interior  are  in  a  condition  of  strain,  and  their  re- 
lease is  the  occasion  of  the  propagation  of  a  series  of 
waves  of  elastic  compression.  The  breaking  in  of  parts 
of  the  crust  through  the  removal  from  below  of  the 
supporting  material,  as  in  the  fall  of  the  roof  of  a  cave, 
is  still  another  cause  of  earthquake-making.  The  dis- 
aster in  the  valley  of  the  Upper  Rhone  in  Switzerland, 
in  1855,  when  the  greater  part  of  the  town  of  Visp 
was  destroyed,  seems  to  have  been  the  immediate  result 
of  a  subsidence  following  the  removal  of  the  underlying 
lime  and  gypsum  deposits  through  solution. 

It  would  appear  that  by  far  the  greater  number  of 
earthquakes,  whether  large  or  small,  have  their  origin 
at  only  a  moderate  depth  beneath  the  surface.  Prob- 
ably from  ten  to  fifteen  miles  measures  the  depth  for 
all,  and  in  the  case  of  many  it  is  unquestionable  that 
they  originate  still  nearer  to  the  surface.  In  the  case 
of  the  Carolina  earthquake  of  1886,  the  depth  of  origin 
is  assumed  to  have  been  about  twelve  miles ;  and  from 
this  point  travelled  out,  in  radiating  lines,  and  at  vary- 
ing angles,  the  series  of  pulsations  which  reached  in 


134  THE  EARTH  AND   ITS   STOUT. 

one  or  more  directions  to  a  distance  of  a  thousand  miles 
or  more.  It  has  been  claimed  for  the  tremors  which 
accompanied  and  followed  the  great  eruption  of  Kra- 
katao,  in  1883,  that  they  were  transmitted  completely 
through  the  earth,  or  across  a  distance  of  upwards  of 
seven  thousand  miles. 

Passage  of  the  Earthquake  Waves.  —  We  do  not  as 
yet  fully  know  all  the  peculiarities  and  eccentricities 
which  associate  themselves  with  the  transmission  of 
earthquake  impulses ;  indeed,  some  of  the  rules  or 
conditions  which  appear  to  be  firmly  established  in  cer- 
tain  regions  are  reversed  elsewhere.  Thus,  it  is  well 
knoAvn  that  in  some  parts  the  accumulation  of  loose 
material,  as  gravel,  sand,  or  soil,  is  a  bar  to  the  pas- 
sage of  an  earthquake,  or  at  least  tends  to  render 
its  force  ineffective;  elsewhere,  it  is  just  this  form  of: 
deposit,  as  distinguished  from  solid  rock,  which  tends 
toward  destructive  results.  But  whether  one  way  or 
another,  it  may  be  laid  down  as  a  rule  that  an  earth- 
quake, issuing  from  one  class  of  deposits,  and  passing 
into  the  other,  will  at  the  line  of  junction  do  its 
severest  work.  The  difficulty  of  accommodation  in 
the  pulsating  waves  to  new  conditions  seems  to  be 
that  which  brings  about  the  disastrous  result.  The 
influence  of  mountain  chains  as  determining  and  direct- 
ing the  passage  of  earthquake  impulses  has  long  been 
recognized ;  the  waves  pass  with  difficulty  through  (or 
across)  them,  while  they  travel  readily  along  the  line 
of  their  extension.  Earthquakes  of  considerable  in- 
tensity originating  on  one  side  of  a  mountain  axis 
may  be  entirely  inappreciable  on  the  opposite  side, 
even  if  removed  only  by  a  few  miles.  In  the  same 


EARTHQUAKE  PHENOMENA.         135 

way  a  void  of  rock  material,  such  as  may  exist  in 
the  region  of  caves,  is  a  bar  to  the  propagation  of 
waves  of  this  class. 

Intensity  of  Movement.  —  Judged  by  ordinary  sen- 
sation the  earthquake  movement  is  an  extensive  one  ; 
we  feel  ourselves  turned  and  twisted,  houses  fall  and 
crumble,  and  the  earth  seems  to  sway  up  and  down 
with  considerable  departure  from  the  horizontal  line. 
Yet  it  is  certain  that  in  by  far  the  greater  number  of 
cases  of  even  fairly  severe  earthquakes  the  actual 
earth  movement,  either  horizontally  or  vertically,  is 
a  very  insignificant  one,  not  measuring  more  than  a 
fraction  of  an  inch.  In  the  disastrous  Neapolitan 
earthquake  of  1857  the  movement  was  determined  to 
be  from  two  to  five  inches.  Our  own  exaggerated 
notions  are  the  result  of  mental  disturbance  for  the 
time,  and  therefore  subjective  in  their  sensation.  It 
is  true,  however,  that  under  exceptional  conditions 
really  extensive  movements  do  take  place,  movements 
which  may  be  of  a  differentially  vertical  nature,  or 
purely  lateral  in  their  effect.  Thus,  it  is  thought  to 
be  beyond  question  that  areas  in  both  Italy  and  Greece 
have  been  dropped  several  feet  as  the  result  of  earth- 
quake action;  and  this  condition  has  been  noted  even 
so  recently  as  the  year  1893,  when  the  Phocian  and 
Athenian  plains  were  so  rudely  shaken.  It  is  stated 
011  fairly  good  authority  that  the  region  of  Casalnuovo, 
in  Calabria,  Italy,  dropped  twenty-nine  feet  in  the  early 
part  of  the  last  century  as  the  result  of  earthquake  dis- 
turbance. Similar  occurrences  have  been  noted  in  the 
Philippines,  in  New  Zealand,  in  the  region  of  western 
California  (also  in  the  water-tract  between  it  and  the 


136  THE  EARTH  AND  ITS   STORY. 

outlying  islands),  and  in  the  middle  Mississippi  basin 
(1811-1812).  Elevation  at  times,  but  less  often,  takes 
the  place  of  depression;  the  western  coast  of  South 
America  is  most  generally  appealed  to  for  evidence 
in  support  of  this  condition,  but  it  is  still  doubtful  if 
the  facts  there  revealed  have  been  properly  interpreted. 
Fissures  of  greater  or  less  length,  and  of  varying  width, 
are  a  frequent  accompaniment  of  earthquake  action ; 
sometimes  they  remain  permanently  open,  but  more 
generally  their  existence  is  only  temporary.  Sand  and 
mud  of  various  degrees  of  consistency  are  frequently 
squeezed  up  in  the  course  of  compression  of  the  earth, 
and  their  appearance  on  the  surface  may  give  rise  to 
local  deposits  of  considerable  magnitude. 

Tidal  Waves.  —  Following  any  extensive  shock  on 
the  ocean-front  is  the  transmission  of  an  ocean  or 
"  tidal "  wave,  the  intensity  and  magnitude  of  which 
will  necessarily  be  determined  by  the  violence  and 
length  of  continuance  of  the  concussion.  The  devas- 
tation caused  by  such  earthquake  waves,  whose  move- 
ment may  be  transmitted  completely  across  the  oceanic 
basin,  is  frequently  far  in  excess  of  that  which  is  pro- 
duced directly  by  the  earth  movement  itself ;  the  waves 
following  in  the  wake  of  the  destructive  earthquake  of 
Lisbon,  in  1755,  broke  over  the  town  to  a  height  of 
30-60  feet  above  highest  tide,  while  those  of  Lupatka 
(October,  1737)  measured  210  feet.  The  waves  which 
followed  the  Krakatao  catastrophe,  and  impinged  upon 
the  East  Indian  coast,  are  said  to  have  swept  43,000 
persons  out  of  existence.  Singularly  enough,  the  ad- 
vent of  an  earthquake  is  at  times  heralded  by  a  reces- 
sion or  withdrawal  of  the  sea ;  such  was  the  case  in 


EARTHQUAKE  PHENOMENA.         137 

1868,  when  the  island  of  St.  Thomas  was  visited;  and 
at  the  time  of  the  earthquake  of  Jamaica,  in  1692,  the 
sea  is  said  to  have  receded  a  full  mile.  No  fully  satis- 
factory explanation  of  this  condition  has  yet  been  given. 
The  rapidity  of  transmission  of  the  earthquake  wave  is 
prodigious  ;  after  the  disturbance  on  the  west  South 
American  coast  in  1868  (earthquake  of  Arica),  the  roll- 
ing swell  made  the  transit  to  Honolulu,  a  distance  of 
5,580  nautical  miles,  in  12  hours  and  37  minutes,  or 
with  an  average  velocity  of  746  feet  per  second.  This 
is  nearly  as  rapid  as  the  transmission  of  the  actual 
earthquake  pulsation  through  the  solid  rock.  The 
Carolina  earthquake  of  1886  is  assumed  to  have  trav- 
elled, in  one  direction  at  least,  at  the  exceptionally 
rapid  rate  of  16,000  feet  (or  three  miles)  per  second; 
the  Tokio  earthquake  of  Oct.  25,  1881,  9,000  feet. 

The  number  of  impulses  that  belong  to  an  earth- 
quake varies.  There  are  usually  a  first  and  a  second 
shock;  but  oftentimes  numbers  of  shocks,  of  greater 
and  less  magnitude,  follow  one  another  in  rapid  suc- 
cession, to  the  extent  of  making  an  almost  continuous 
earthquake  of  hours'  or  days'  duration.  At  St.  Thomas, 
in  1868,  two  hundred  and  eighty  shocks  were  experi- 
enced in  about  as  many  hours ;  and  in  New  Zealand,  in 
1848,  it  is  claimed  that  for  a  period  of  a  week  or  more 
the  shocks  were  transmitted  at  the  rate  of  a  thousand 
per  day.  Again,  the  earthquake  which  visited  Japan 
in  the  year  977  is  said  to  have  extended  over  a  period 
of  three  hundred  days. 


138  THE  EARTH  AND  ITS   STORY. 


CHAPTER   XII. 

CORALS    AND    CORAL    ISLANDS. 

THE  coral  cluster  that  gracefully  adorns  our  mantel- 
tops  is  not  usually  viewed  in  the  light  of  a  geological 
specimen ;  it  is  an  animal,  and  its  history  is  a  part  of 
that  of  the  organic  chain.  In  reality,  however,  geology 
can  claim  the  greater  part  of  this  history,  since  it  is  in 
its  association  with  the  rock-formations  of  the  globe 
that  the  lowly  organism  teaches  its  most  pregnant  les- 
son. Few  there  are  among  the  thousands  who  annually 
visit  the  lovely  Bermuda  Islands,  or  the  less  distant 
Bahamas,  with  their  flecks  and  strips  of  gray  sand, 
their  wind-swept  knolls  and  undulating  hillocks,  who 
realize  the  significance  of  the  landscape  that  is  before 
them ;  the  wonderfully  tinted  waters,  the  peculiar  vege- 
tation of  sub-tropical  aspect,  the  pleasurable  climate,  — 
these  are  all  elements  that  appeal  directly  to  the  ar- 
thetic  sense,  but  they  reveal  little  of  the  history  that  is 
bound  in  with  them. 

The  Aspects  of  a  Coral  Reef.  —  To  understand  prop- 
erly what  a  coral  island  really  is,  and  how  it  is 
manufactured,  one  has  to  visit  that  part  of  the  sea 
immediately  about  it,  wherein  the  coral  animal  is  work- 
ing and  luxuriating  —  the  coral  reef.  It  is  there  that 
the  material  is  being  prepared  for  future  rock-con- 
struction, there  that  a  battle  is  constantly  being  waged 


Plate  45. 


CORALS  AND  CORAL  ISLANDS. 


1 .  The  aeolian  coral-sand  rock  of  the 

2.  A  portion  of  the  coral-reef  kncv 

the  closely  matted  and  coi  " 
"brain-corals." 


.wind-drift  stratification. 

Keef  of  Australia,  s'<owiiio: 
j£  corals.    The  rounded  masses  are 

UNIVERSITY    1 

OF  / 


Plate  46. 


CORALS  AND  CORAL  ISLANDS. 

1.  A  fan  coral,  Rhipidogorgia,  from  the  Bermuda  reefs. 
9.  A  portion  of  a  brain-coral,  Mxandrina. 


CORALS  AND   CORAL  ISLANDS.  139 

between  the  organic  and  the  inorganic  forces  for  su- 
premacy and  possession  of  the  sea.  My  own  first  im- 
pressions of  the  growing  reef  were  obtained  at  a  lonely 
locality,  removed  about  nine  miles  to  the  northward  of 
the  Bermuda  Islands,  and  known  as  the  North  Rock. 
This  North  Rock  is,  in  fact,  an  assemblage  of  three 
or  four  small  rock-pinnacles,  which  in  low  water  show 
themselves  to  be  united  by  a  connecting  base,  but  in 
high  water  stand  separate,  each  for  itself.  Standing 
on  this  connecting  base,  and  looking  over  to  the  ocean 
side,  one  sees  a  wonderful  assemblage  of  living  animal 
forms,  the  greater  number  of  which  are  clumps  and 
heads  of  various  kinds  of  coral,  some  small,  others 
measuring  several  feet  across ;  luxuriating  near  the  sur- 
face of  the  water,  and  in  their  various  colors  and  shades 
of  orange,  green,  brown,  and  purple,  they  are  spread 
out  before  the  eye  like  the  pattern  of  a  mosaic  pave- 
ment. Well  in  among  these  coral  masses  are  a  mul- 
titude of  sponges,  —  black,  yellow,  and  vermilion,  — 
various  coralloids  (millepores),  sea-fans,  and  squirts,  all 
of  them  firmly  attached  like  the  corals  themselves,  while 
between  them  run  about  an  army  of  crabs,  of  colors 
hardly  less  brilliant  than  those  of  their  immediate  sur- 
roundings. A  variety  of  shells  is  invariably  associated 
with  the  growing  reef,  and  in  the  numerous  holes  and 
crevices  the  eye  cannot  fail  to  detect  the  spines  or  hard 
cases  of  a  number  of  sea-urchins.  This  is,  in  a  general 
way,  the  composite  picture  of  a  coral  reef,  a  type  of 
very  nearly  all  of  its  class,  but  which  carries  with  it  no 
conception  of  the  rapturous  beauty  of  its  construction. 
No  flower-garden  of  the  earth  surpasses  it  in  wealth  of 
kaleidoscopic  coloring ;  and  it  may  justly  be  doubted  if 


140  THE  EARTH  AND  ITS   STORY. 

any  approaches  it,  for  the  silvery  texture  of  the  over- 
lying water  adds  a  luminosity  and  brilliancy  to  the 
scene  for  which  neither  the  calm  atmosphere  nor  the 
warm  sunshine  can  offer  a  substitute.  To  have  seen 
the  world  without  having  visited  a  coral  reef  is  to 
have  seen  a  picture  with  the  best  of  its  coloring  left 
out.  (Plate  45,  Fig.  2  ;  Plates  46,  47.) 

The  Making  of  Coral  Land.  —  All  the  active  life  of 
the  coral  is  carried  on  within  a  few  feet  of  the  water's 
surface,  for  there  is  only  a  limited  number  of  the  reef- 
buildirig  species  which  thrive  at  a  greater  depth  than 
15  or  30  feet:  some  types  live  with  a  certain  amount 
of  luxuriance  down  to  80  or  100  feet,  a  few  even  at 
300  or  400  feet;  but  by  far  the  greater  number  are  con- 
fined to  the  upper  zone,  where  there  is  a  strong  pene- 
tration of  sunlight.  They,  moreover,  require  a  mild 
temperature,  one  that  rarely  descends  below  68°  or 
60°  F.  This  condition  restricts  the  distribution  of  the 
reef-building  corals  to  a  nearly  tropical  or  sub-tropical 
zone,  and  there  are  but  few  instances  where  there  is  a 
marked  transgression  beyond  this  zone  (Bermudas ;  Quel- 
paert's  Island,  near  Corea).  Wherever  the  polyps  build 
close  to  the  surface,  their  habitations  are  attacked  by 
the  surf  which  they  themselves  create.  The  long  white 
line  of  foam  which  meets  the  eye  of  the  observer  gaz- 
ing off  from  any  of  the  eminences  of  such  an  island 
group  as  the  Bermudas,  and  which  parts  the  blue  waters 
of  the  outer  world  from  the  more  nearly  green  within, 
is  but  the  line  of  battle  between  the  organic-  and  the  in- 
organic forces.  Blocks  of  coral  and  coralline  are  de- 
tached and  broken,  their  parts  are  rocked  to  and  fro  in 
the  withering  crest,  and  ultimately,  when  the  fragments 


Plate  47. 


CORALS  AND  CORAL  ISLANDS. 
1.  Rose  coral  (I soph yllia).      2.  Branch  of  Oculina.      3.  Miliepore  (right-hand  figure). 


CORALS  AND   CORAL   ISLANDS.  141 

have  been  sufficiently  punished  by  the  sea,  they  are 
handed  over  for  further  chastisement  to  the  action  of 
the  wind.  In  this  way  the  particles  are  ground  finer 
and  finer,  true  sand  is  formed,  and  dunes  begin  to  rear 
their  heads  above  the  ocean  level.  Travelling  in  the 
line  of  the  wind,  the  dunes  pass  onward,  climb  over  one 
another's  backs,  and  comb  the  gently  flowing  crests ; 
from  pygmy  hillocks  they  rise  into  well-fashioned  knolls, 
and  ultimately  stand  as  eminences,  such  as  are  to-day 
the  Bermudas.  No  one  who  has  watched  the  great 
tongues  of  moving  sand  stealthily  encroaching  over  the 
hilltops  of  the  interior,  and  burying  everything,  in  the 
manner  of  the  locusts  of  South  Africa,  beneath  their 
mantle  of  destruction,  can  have  failed  to  be  impressed 
with  the  character  and  the  magnitude  of  the  work  that 
is  being  accomplished.  It  is  nothing  but  the  music  of 
the  sea  and  wind,  but  there  is  enough  of  it  to  turn 
water  into  land. 

This,  then,  is  a  coral  island.  It  has  its  caves,  lagoons, 
and  separating  watercourses,  —  its  flat  reaches  of  coral 
sand  and  shell,  its  hills  and  hummocks  and  sea-cliffs. 
The  decaying  rock  has  made  soil,  and  over  it,  perhaps, 
has  spread  a  vegetation  of  soft  luxuriance,  elsewhere 
scraggy  and  deficient  in  noble  character.  The  wind- 
drift  or  seolian  character  of  the  rocks  is  everywhere 
apparent ;  along  the  roads,  on  the  hillsides,  and  in  the 
caves,  we  find  the  same  rock  made  up  of  organic  parti- 
cles. The  layers  or  seams,  inclining  now  one  way,  now 
another,  point  to  the  different  positions  into  which  the 
sand  has  been  fortuitously  cast  by  the  winds,  patted 
down,  and  built  up  into  a  series  of  superimposed  layers. 
Shells,  both  marine  and  terrestrial,  have  been  caught  in 


142  THE  EARTH  AND  ITS  STORY. 

the  drifts,  for  we  find  them  imbedded  in  the  rock,  and 
scattered  up  to  a  height  of  200  feet.  (Plate  45,  Fig.  1.) 
The  Kinds  of  Coral  Islands.  —  The  type  of  coral 
island  that  has  here  been  described  is  that  which  is 
represented  in  the  Bermudas,  the  Bahamas,  and  the 
Florida  Keys.  Briefly  characterized,  they  are  consoli- 
dated heaps,  50  to  260  feet  high,  of  coral  and  coralline 
fragments  or  sand,  which  have  been  tossed  up  by  the 
wind,  and  whose  origin  is  the  growing  reef  outside. 
Irregular  bodies  of  water  —  lagoons  or  sounds  —  scatter 
themselves  about  the  separated  patches  or  islets,  and  in 
them,  too,  is  a  fairly  luxuriant  coral  growth.  As  dis- 
tinguished from  this  simple  type  —  although  in  some 
instances  only  a  modification  of  it  —  are  the  forms 
known  &&  fringing  reefs,  where  the  coral  structures  hug 
pretty  closely  a  more  or  less  extended  coastline ;  bar- 
rier reefs,  where  these  structures  follow  the  trend  of  a 
coast,  but  are  yet  separated  from  it  by  a  narrow,  often- 
times very  profound,  body  of  water.  The  Great  Aus- 
tralian Barrier  Reef  is  usually  described  as  a  nearly 
continuous  reef  structure  about  a  thousand  miles  in 
length,  with  a  separating  width  of  water  ranging  to 
fifty  miles,  and  with  a  depth  of  350  feet.  Other  forms 
are  atolls,  or  ring  islands,  where  the  construction  is  in 
the  form  of  a  narrow  ring  or  collar  of  living  and  dead 
coral,  encircling  a  central  lagoon,  50  to  300  feet  in 
depth.  This  lagoon,  like  the  inner  waters  of  barrier 
reefs,  is  kept  in  communication  with  the  outer  body  of 
the  ocean  by  means  of  one  or  more  channels  breaking 
through  the  coral  wall.  In  all  these  various  forms 
of  coral  structure  the  same  fundamental  principles  of 
development  govern  the  making  —  corals  growing  in 


CORALS  AND   CORAL   ISLANDS.  148 

shallow  water,  breakage  through  the  action  of  the 
waves  and  surf,  and  the  heaping  up  and  distributing 
of  the  materials  derived  from  destruction  ("  coral 
sand  ")  through  wind-action.  There  are,  however,  cer- 
tain phases  in  the  life-history  of  coral  islands  which  have 
a  special  significance  of  their  own,  and  a  bearing  upon 
broad  questions  in  geology  which  gives  to  them  a  par- 
ticular importance.  We  shall  turn  to  an  examination 
of  some  of  these. 

Occurrence  in  Deep  Water;  Formation  of  Reefs. - 
Nothing  strikes  the  investigator  more  strange  than  the 
fact  that,  while  the  reef-building  corals  themselves  live 
only  in  shallow  water,  their  structures  seemingly  rear 
themselves  up  from  the  profoundest  depths  of  the 
ocean.  Thus,  within  a  few  hundred  yards  off  the 
bounding  reefs  of  the  Bermudas,  the  lead  drops  a  thou- 
sand feet  and  more,  and  at  a  distance  of  some  seven 
miles,  it  drops  to  12,000  feet.  Were  the  full  height 
of  the  island-group  visible  from  this  side,  it  would 
present  the  appearance  of  a  huge  rock  buttress,  the 
like  of  which  could  hardly  be  matched  among  the 
mountains  of  the  dry  land.  Similar  sudden  plunges 
associate  themselves  with  coral  islets  of  the  Pacific 
basin;  and  in  a  few  instances  it  is  claimed  —  although 
the  fact  perhaps  requires  further  confirmation  —  that 
the  descent  for  considerable  distances  is  well-nigh  ver- 
tical, or  absolutely  so.  It  would  thus  appear  that  the 
coral-made  rock  is  one  of  very  considerable  thickness, 
of  far  greater  development  than  would  be  permitted 
by  the  shallow  zone  in  which  the  polyps  live  and  build. 
Hence,  we  naturally  ask  ourselves  :  Under  what  special 
conditions  can  this  apparently  thick  rock  form  ? 


144  THE  EARTH  AND   ITS   STORY. 

To  the  genius  of  the  late  Mr.  Darwin  we  owe  the 
explanation,  combated  in  some  quarters  of  late,  but 
which  has  most  generally  been  received  by  geologists. 
He  assumed  that,  in  all  regions  where  the  corals  built 
up  from  deep  water,  we  had  positive  evidence  of  sub- 
sidence in  the  trough  of  the  sea.  The  sinking  of  the 
fundament  carried  with  it  the  already  made  rock,  and 
allowed  new  material  to  be  built  up  or  accumulated 
with  equal  rapidity  on  the  descending  surface.  In  this 
way  the  working  corals  were  steadily  being  submerged 
beneath  the  proper  zone  of  their  existence ;  their  ac- 
tivity ceased,  and  the  living  rock  became  converted 
into  "  dead "  material ;  but  the  more  favored  portion 
of  the  community  worked  busily  onward  on  the  top, 
and.  filled  up  the  space  that  was  continuously  open  to 
them  in  the  shallows  of  sixty  to  one  hundred  feet 
depth.  It  will  readily  be  seen  that  through  this  pro- 
cess of  sinking  at  the  bottom  and  growing  on  the  top, 
an  almost  endless  thickness  of  rock  might  in  course  of 
time  be  formed. 

Thickness  of  Coral-Made  Rock ;  Subsidences.  —  It 
is  still  an  open  question  with  many  geologists  whether 
or  not  coral  rock  has  anywhere  the  very  great  thick- 
ness that  has  been  assumed  for  it  in  many  cases ;  if  it 
has  not,  there  is  no  need  to  invoke  the  assistance  of 
subsidence  to  account  for  the  phenomena  as  they  pre- 
sent themselves.  Some  geologists  have  argued,  and 
still  argue,  that  the  coral  islets  —  like  those  of  the 
Pacific  basin  —  which  rise  with  such  sudden  steepness 
from  the  deep  hollow  of  the  ocean,  are  merely  thin 
"  cappings "  perched  upon  the  crater-heads  of  sub- 
merged volcanoes ;  others  maintain  that  they  are  only 


CORALS  AND   CORAL   ISLANDS.  145 

the  final  deposit  of  organic  material  which  has  accumu- 
lated on  banks  that  have  been  built  up  in  part  mechani- 
cally, and  in  part  by  organic  agencies  other  than  those 
of  coralline  life  —  that  is,  by  animal  types  whose  activity 
is  not  limited  to  the  shallow  zone  of  sixty  or  one  hun- 
dred feet.  To  both  of  these  suppositions  the  only 
answer  that  can  be  given  is  that  they  remain  in  the 
nature  of  hypotheses  ;  no  such  array  of  submerged 
volcanic  peaks  as  would  be  found  necessary  to  account 
for  the  numerous  coral  islands  and  islets  that  dot  the 
Pacific  has  been  shown  to  exist  —  in  fact,  it  is  almost 
certain  that  they  do  not  exist;  nor  has  it  been  shown 
that  any  extensive  banks,  except  possibly  near  the 
shore  in  the  line  of  the  continental  sediment,  have  ever 
been  reared  up  in  the  manner  that  has  been  assumed, 
through  thousands  of  feet  of  oceanic  water.  The 
Florida  reefs  and  the  Bahamas  may  in  part  lie  on  such 
mechanically  and  organically  constructed  platforms,  but 
their  continental  position  is  special  to  themselves,  and 
hardly  permits  a  bearing  on  the  general  question.  On 
the  other  hand,  it  is  positively  known  that,  in  some 
instances  at  least,  the  solid  coral  rock  has  a  thickness 
of  three  hundred  or  four  hundred  feet,  and  therefore 
much  exceeds  the  development  that  would  be  permitted 
were  there  no  subsidence  ;  and  further,  it  is  equally 
certain,  and  proved  by  evidence  of  a  very  different  kind, 
that  subsidences  have  taken,  and  are  still  taking,  place 
in  regions  where  many  of  the  coral  reefs  and  islands 
are  situated. 

The  Atoll  Lagoon.  —  One  of  the  most  perplexing 
features  of  coral  islands  is  the  deep  central  depression, 
the  lagoon  of  the  atoll.  We  have  seen  that  it  has 


146  THE  EARTH  AND   ITS   STOEY. 

a  depth  ranging  anywhere  from  a  few  feet  to  sev- 
eral hundred  feet;  therefore  it  extends  far  below  the 
zone  of  the  living  animal.  By  Mr.  Darwin,  and  his 
followers  of  the  "  subsidence  "  school,  it  was  held  to 
represent  the  position  of  a  piece  of  land-area  around 
which  the  coral  animals  had  primarily  established  them- 
selves, and  which  in  course  of  time  disappeared  by 
sinkage.  When  yet  at  the  water-surface,  with  the 
corals  working  around  it,  it  was  separated  from  the 
forming  reef  by  a  circle  of  water,  which  was  kept 
barren  of  coral  habitations  through  the  condition  that 
the  reef-building  coral  does  not  thrive  in  muddy  water, 
or  in  water  that  receives  the  down-wash  off  decaying 
land-masses.  As  subsidence  proceeded,  the  belt  of  sepa- 
rating water  became  progressively  larger,  until  finally, 
with  the  full  disappearance  of  the  land,  it  occupied  the 
entire  space  included  between  the  outside  ring  of  coral. 
Thus  was  brought  about  the  crateral  hollow  with  its 
occupying  waters.  By  some  geologists  it  has  been 
assumed  that  the  hollow  may  have  been  occasioned 
by  chemical  dissolution  of  the  lime ;  but  it  is  certain 
that  whatever  amount  is  actually  removed  in  this  way, 
and  there  may  be  much  of  it,  it  is  more  than  compen- 
sated for  by  the  debris  that  accumulates  within  the 
basin  itself  as  the  result  of  rock-wear  and  breakages. 
Elevated  Reefs.  —  In.  many  oceanic  islands  there  is 
direct  evidence  to  the  fact  that,  instead  of  subsidence 
having  taken  place,  elevation  has  been  the  order  of 
movement,  at  least  a  late  phase  of  it.  AVe  find  coral 
reefs  that  are  to-day  high  and  dry,  and  yet  we  know 
that  when  they  were  being  constructed  they  were  in 
the  water.  Such  raised-reef  structures  border  a  con- 


CORALS  AND    CORAL   ISLANDS.  147 

siderable  extent  of  the  island  of  Cuba,  and  are  like- 
wise found  in  Jamaica,  in  the  Solomon  Islands  of  the 
Pacific,  etc.  The  fact  of  their  being  elevated  has 
little  or  no  bearing  upon  the  general  question  of  coral 
constructions ;  since,  even  if  we  have  to  admit  prodi- 
gious subsidence  to  explain  the  seemingly  anomalous 
position  of  the  almost  innumerable  coral  islands  of  the 
Pacific  Ocean,  there  is  nothing  to  preclude  the  possi- 
bility, or  even  easy  probability,  of  an  elevatory  move- 
ment having  followed  that  of  subsidence.  Nor  are 
any  geological  facts  opposed  to  the  notion  that  move- 
ments of  both  elevation  and  depression  may  take  place 
simultaneously,  and  side  by  side,  in  regions  of  moderate 
extent.  Caution  should  here  be  emphasized  as  to  the 
proper  interpretation  of  the  terms  subsidence  and  ele- 
vation. It  is  by  no  means  unlikely  that  what,  in  many 
cases,  we  assume  to  be  "subsidence"  of  the  land  is 
merely  a  rise  of  the  oceanic  waters  ;  a"nd,  conversely, 
the  "  rise  "  of  the  land  may  be  only  a  falling-ofT  of  the 
oceanic  waters.  The  records  or  marks  that  would  be 
left  by  either  one  construction  or  the  other  would  be 
fundamentally  the  same  ;  and  there  are  many  reasons, 
as  have  already  been  stated,  for  assuming  a  decided 
instability  in  the  level  of  the  oceanic  surface. 

Distribution  of  Modern  Reefs.  —  Nearly  all  the  reefs 
of  to-day  are  confined  within  the  zone  of  twenty-five 
degrees  north  and  south  of  the  equator.  .  They  are 
most  largely  developed  in  the  Indian  Ocean  and  in  the 
Australian  and  Polynesian  Seas  ;  the  greater  number 
of  the  archipelagic  islands  of  the  Pacific  are  in  them- 
selves of  coral  origin  (like  the  Paumotu,  Carolines, 
Gilbert,  and  Iladack  Islands),  or  volcanic,  with  sur- 


148  THE  EARTH  AND  ITS   STORY. 

rounding  areas  of  reefs  (Tahiti,  Samoa,  Feejee,  Hawaii). 
The  larger  Sunda  Islands  —  Borneo,  Celebes,  Java,  Su- 
matra —  are  almost  destitute  of  coral  structures,  prob- 
ably a  result  of  the  intensity  of  volcanic  action  in  the 
region.  Reefs  are  abundant  in  the  Red  Sea,  and  are 
found  at  intervals  on  the  East  African  coast,  extending 
opposite  Port  Natal  to  the  30th  parallel  of  south  lat- 
itude. In  the  Atlantic  basin  we  have  the  Bermudas, 
Bahamas,  Florida  Keys,  and  the  general  West  Indian 
region,  together  with  scattered  formations  north  and 
west  of  Yucatan,  and  in  the  off-shore  of  the  Gulf  of 
Mexico  (Vera  Cruz).  Almost  the  entire  west  coast 
of  America  is  free  from  these  habitations. 

Ancient  Reefs. -- There  is  plenty  of  evidence  in  the 
rocks  to  show  that  reef-structures  of  one  kind  or 
another  were  extensively  developed  throughout  nearly 
all  the  periods  of  geological  time,  and  in  many  of 
them  on  a  seemingly  much  more  gigantic  scale  than 
at  the  present  time.  Furthermore,  their  development 
was  not  restricted  to  the  comparatively  narrow  geo- 
graphical zone  to  which  the  energies  of  coral  life  are 
to-day  confined;  but  it  extended  far  toward  what  is 
now  the  Arctic  realm,  and  in  some  regions  well  within 
it.  Ancient  reef-structures  have  been  noted  in  Russia 
and  in  Scandinavia  far  beyond  the  60th  parallel  of 
latitude,  some  of  the  reef-building  types  of  coral  having 
left  their  impress  in  the  rocks  of  Spitsbergen  and  Nova 
Zembla  ;  indeed,  much  the  same  forms  were  obtained  by 
the  British  North  Pole  Expedition  of  1875-1876  from 
a  point  on  the  American  side  beyond  the  82d  parallel 
of  latitude.  These  facts  make  it  certain  that  the  ther- 
mal conditions  of  the  northern  waters  were  very  differ- 


CORALS  AND   CORAL   ISLANDS.  149 

ent  from  what  they  now  are ;  probably  the  temperature 
was  very  much  higher,  generally  equable,  and  more 
like  what  we  have  to-day  in  the  tropical  and  subtropi- 
cal zones.  Yet  we  are  by  no  means  certain  that  the 
climate  was  in  fact  like  that  of  our  southern  regions, 
as  the  types  of  the  ancient  corals  are  largely  different 
from  that  now  existing ;  and  the  conditions  governing 
their  existence  may  have  varied  essentially  from  those 
that  regulate  the  coral  life  of  the  modern  seas. 


150  THE  EARTH  AND  ITS   STORY. 


CHAPTER    XIII. 

FOSSILS    AND    THEIR    TEACHINGS. 

What  a  Fossil  is.  --There  are  not  very  many  things 
more  difficult  to  define  than  fossils.  Ordinarily,  they 
are  assumed  to  be  organisms,  or  remains  of  organisms, 
which  have  for  some  time  been  buried  in  rock,  mud, 
or  clay,  and  become  "  petrified,"  i.e.,  turned  into  stone. 
This  definition  probably  explains  a  large  number  of 
cases  of  fossilization,  but  by  no  means  all ;  for  in  very 
many  instances  what  geologists  term  fossils  have  in  no 
way  become  truly  petrified.  Skeletons  remain  as  dis- 
tinctly bony  as  they  ever  were,  without  perhaps  mate- 
rial change  of  any  kind  having  taken  place  within 
them;  again,  any  number  of  " fossil"  shells  are  in 
no  Avay  different  in  character  or  structure  from  their 
allies  or  representatives  living  to-day.  In  the  broadest 
definition,  it  may  be  said  that  everything  is  fossil  that 
leaves  an  impression  in  the  materials  of  a  clearly  de- 
fined rock,  sand,  or  mud  formation,  provided  this  for- 
mation is  not  merely  one  of  our  own  immediate  time. 
Hence,  fossils  can  be  millions  of  years  old,  or  have 
existed  only  a  few  hundred  years,  or  even  less ;  the 
more  recent  ones  are  frequently  termed  sub-fossils. 
Again,  not  only  are  animals  and  plants,  and  their  im- 
pressions (footprints,  etc.),  fossils,  but  many  inanimate 
objects  or  their  marks  are  also  classed  as  such ;  thus  we 


Plate  52. 


A  block  of  rock  crowded  with  Ammonites;  a  piece  of  fossilized  wood  shows  in  the  left. 
From  the  Jurassic  deposits  of  England. 


OF   THE 

UNIVERSITY 

OF 


FOSSILS  AND   THEIR   TEACHINGS.  151 

speak  of  "  fossil  raindrops,"  "  fossil  ripple-marks,'' 
"fossil  sun-cracks,"  and  even  of  "fossil  glaciers."  In 
the  following  pages,  the  discussion  of  fossil  remains 
will  be  restricted  to  the  belongings  of  the  organic 
world  (animals  and  plants).  (Plates  5,  6.) 

Manner  of  Occurrence  of  Fossils.  —  It  stands  to  rea- 
son that,  generally,  the  older  the  fossil,  the  more  does 
it  depart  in  texture,  form,  and  color  from  the  original 
of  which  it  constitutes  the  remains.  Sometimes  the 
body  or  shell  structure  has  been  completely  removed, 
and  in  its  place  we  find  stone  ;  at  other  times,  with 
shells,  for  example,  these  parts  are  not  retained  at  all, 
and  we  have  as  fossils  only  the  impressions  made  by 
the  outside  of  the  shell,  or  the  filling  in  of  the  cavity 
of  the  shell  itself,  —  "  impressions,"  "  moulds,"  and 
"  casts."  It  is  not  often  that  the  soft  parts  of  an  animal 
are  preserved,  either  by  substitution  or  otherwise,  as 
decomposition  and  decay  remove  them  too  rapidly  to 
permit  of  preservation ;  still,  a  few  such  instances  are 
known,  as,  for  example,  the  mammoths  of  the  north 
Siberian  ice-plains,  the  skin  and  muscle  (strictly  petri- 
fied) of  certain  ancient  reptiles,  and  the  stone-flesh  of 
some  shellfish.  The  so-called  stone-men  of  sensational 
museums  have  nothing  in  common  with  this,  and 
represent  merely  hardened  tissues  due  to  a  special 
development  of  adipocere.  Fossil  man  exists  only  as 
skeleton,  and  through  his  belongings  in  the  form  of  crude 
implements,  "  kitchen  middens,"  "  charcoal  heaps,"  etc. 

There  are  a  number  of  instances  where  the  color- 
markings  on  shells  have  been  retained  through  an 
astonishingly  long  period,  believed  by  many  to  be  a 
million  years  or  more.  It  is  indeed  difficult  to  realize 


152  THE  EARTH  AND  ITS  STORY. 

such  a  condition ;  but  the  facts  speak  for  themselves, 
and  permit  of  no  contradiction.  The  most  delicate 
plant  structures,  as  we  find  them  in  the  coarser  vein- 
ings  of  leaves,  or  in  the  hairy  down  of  others,  have 
been  similarly  preserved  as  impressions  in  the  rock,  and 
certainly  through  a  score  of  millions  of  years.  Even 
the  delicate,  one  might  say  evanescent,  impression  of 
the  jelly-fish  has  been  preserved  for  much  of  this  length 
of  time.  Naturally,  for  every  specimen  or  impression 
that  has  been  retained,  there  are  thousands,  doubtless 
tens  of  thousands,  which  have  gone  their  way,  and  left 
no  mark  of  their  existence  to  instruct  or  puzzle  the 
geologist. 

Progression  in  Structure.  —  Fossils  of  one  kind  or 
another,  and  of  one  form  or  another,  are  found  in  all 
rock-formations  down  to  the  fundamental  gneiss  and 
schist  —  consequently,  down  to  what  some  geologists 
(probably  more  wrongly  than  rightly)  have  considered 
to  be  the  foundation-stone  of  the  earth's  crust.  Not 
that  fossils  are  necessarily  to  be  found  in  every  rock- 
specimen  that  is  taken  up,  or  even  in  every  mile  of 
rock-surface,  inasmuch  as  their  traces  may  have  been 
locally  obliterated ;  but  somewhere  or  other,  whether 
it  be  in  England,  or  Germany,  or  China,  or  the  north  of 
Pennsylvania,  or  Alabama,  they  do  occur  in  the  deposits 
of  all  ages  down  to  the  schist  or  gneiss,  and  there  are 
excellent  grounds  for  believing  (although  no  positive 
proof  of  this  supposed  fact  has  yet  been  brought  to 
light)  that  life  extended  almost  immeasurably  beyond 
the  time  which  marks  the  appearance  of  the  first  trace 
of  organism. 

The  most  significant  fact  that  is  taught  us  by  the 


FOSSILS  AND    THEIR    TEACHINGS.  153 

millions  of  fossil  forms  that  have  been  preserved  is, 
that  there  has  been  a  steady  and  progressive  advance 
in  the  general  type  of  organization  from  the  oldest 
to  the  newest  periods ;  that  more  highly  developed 
or  more  complicated  forms  have  successively  replaced 
forms  of  simpler  construction;  and  that  this  advance 
is  still  continuing  to-day.  In  the  oldest  rocks,  for 
example,  no  trace  of  backboned  animals  has  yet  been 
detected;  when  such  do  appear  for  the  first  time,  they 
show  themselves  in  their  lowest  types,  the  fishes  ;  these 
are  succeeded  later  by  the  amphibians  (frogs,  newts, 
salamanders),  and  these  again  by  the  reptiles.  And 
if  we  take  the  fishes  by  themselves,  we  find  that  they, 
too,  begin  with  their  lower,  if  not  absolutely  the  lowest, 
types,  and  progressively  develop  their  higher  ones. 
This  history  is  repeated  in  the  cases  of  the  reptiles 
and  quadrupeds  —  in  fact,  with  every  class  of  animals 
that  is  known  to  us.  Naturalists  are  to-day  well 
agreed  among  themselves  that  all  animal  and  vegetable 
forms  are  derivatives  from  forms  that  preceded  them; 
that  however  varied  and  manifold  the  types,  these 
types,  in  hundreds  of  thousands,  have  been  brought 
about  by  slow  processes  of  modification,  acting  through 
ages  of  time,  of  a  limited  number  of  initial  organisms. 
This  is  the  substance  of  the  "  doctrine  of  evolution," 
the  doctrine  which  sees  in  the  origin  of  species  not 
special  creative  acts,  but  merely  the  effects  of  time  and 
surroundings  as  producing  new  and  distinct  forms. 
Hence  it  is,  that,  in  following  the  geological  record, 
we  speak  of  progressive  evolution,  the  evolving  of 
higher  or  more  complicated  types  of  organisms  from 
those  simpler  and  more  general  in  structure. 


154  THE  EAETH  AND   ITS   STOEY. 

The  Time-Standard  of  Geological  History. — The  law 
of  progressive  development  appears  to  have  been 
largely  the  same  for  equal  periods  of  time  all  over 
the  earth's  surface ;  identical  or  closely  related  types, 
if  they  appear  at  all,  appeared  in  much  the  same  time, 
perhaps  varying  in  a  few  thousand  years,  at  all  points 
of  the  globe.  This  fact  has  permitted  geologists  to 
mark  off  distinct  eras  or  periods  in  the  life-history  of 
the  planet,  each  of  them  determined  by  certain  char- 
acteristic animal  or  vegetable  forms,  which  either  do 
not  appear  before  or  after  such  period,  or  else  are  by 
numbers  so  distinctive  of  it  as  to  typify  it  clearly.  - 
Thus,  we  speak  of  an  age  of  trilobites,  of  fishes,  of 
reptiles,  etc.,  meaning  that,  at  the  times  so  designated, 
such  and  such  animals  were  especially  abundant,  or, 
at  least,  were  abundant  in  comparison  with  other  forms. 
Again,  major  divisions  of  time  have  been  further 
divided  into  minor  ones,  to  which  also  special  features 
are  given  by  their  respective  faunas  and  floras.  The 
rocks  that  belong  to  definitely  marked  periods  of  time 
are  naturally  designated  by  the  general  name  of  the 
time-period ;  for  example,  the  rocks  of  the  coal  or 
Carboniferous  period  are  known  under  the  compre- 
hensive name  of  the  Carboniferous  formation  ;  and  so 
the  rocks  of  the  chalk  or  Cretaceous  period  constitute 
the  Cretaceous  rocks,  deposits,  strata,  or  formation. 

The  following  table  represents  pretty  nearly  the 
general  view  of  geologists  as  regards  the  main  divisions 
of  time  and  formations ;  in  it  are  shown  the  more 
distinctive  animal  types  that  characterize  the  different 
eras,  and  the  (approximately)  greatest  thickness  of 
rock  that  was  formed  in  each  interval  of  time :  — 


FOSSILS  AND  THEIR  TEACHINGS. 


155 


Azoic.  Paleozoic  or  Primary.  Mesozoic  or  Secondary.  Cainozoic  or  Tertiary. 

/ 

V 
r 
; 

Epochs 
and  Formations. 

Faunal  Characters. 

POST-PLIOCENE. 
Glacial  Period. 

PLIOCENE.    3.OOO  ft. 
MIOCENE,     s.oooft. 

OLIGOCENE. 
8,000  ft. 

EOCENE.     10,000  ft. 

Man  (not  improbably  earlier).  Mammalia 
principally  of  living  species.  Extinction  of 
Mammoth  and  Mastodon.  Mollusca  almost 
exclusively  recent. 

Mammalia  principally  of  recent  genera  —  liv- 
ing species  (hippopotamus)  rare.  Introduc- 
tion of  the  sheep,  goat,  ox,  bear,  camel, 
macaque.  Mollusca  very  modern. 

Mammalia  principally  of  living  families  :  ex- 
tinct genera  (Mastodon,  sabre-tooth  Cats) 
numerous  ;  species  all  extinct.  Introduction 
of  the  hedgehog,  mole,  porcupine,  beaver, 
squirrel,  rabbit,  tapir,  rhinoceros,  hippopota- 
mus, hog,  deer,  giraffe,  elephant,  cat,  dog, 
hyena  —  not,  however,  of  living  species.  Mol- 
lusca largely  of  recent  species. 

Mammalia  with  numerous  extinct  families  and 
orders  ;  all  the  genera  (with  two  or  three  pos- 
sible exceptions  —  bat,  opossum)  and  species 
extinct.  Modern  type  Shell-Fish. 

Lavamie.       S.OOOft. 

Passage  Beds  between  Cretaceous  and  Eocene. 

CRETACEOUS. 
12.OOO  ft. 
Chalk. 

JURASSIC.    6,000  ft. 
Oolite. 
Lias. 

TRIAS.    25,000(?)ft. 
New  Red  Sandstone. 

Dinosaurian  (bird-like)  Reptiles  ;  Pterodactyls 
(flying  Reptiles)  ;  toothed  Birds  ;  earliest 
Snake  ;  bony  Fishes  very  abundant  ;  Croco- 
diles; Turtles;  Ammonites  (with  almost  final 
extinction)  ;  Deciduous  Trees. 

Earliest  Birds  ;  Archaeopteryx  ;  giant  Reptiles 
(Ichthyosaurs,  Dinosaurs,  Pterodactyls)  ; 
earliest  bony  Fishes  ;  Ammonites  ;  Clam- 
arid  Snail-Shells  very  abundant  ;  decline  of 
Brachiopods  ;  Butterfly. 

First  Mammalian  (Marsupial?)  ;  2-gilled  Ceph- 
alopoda (Cuttle-Fishes,  Belemnites)  ;  reptil- 
ian Foot-Prints  ;  Bird  Foot-Prints? 

PERMIAN.    5.OOO  ft. 

CARBONIFEROUS. 
26,000  ft. 
Coal. 

DEVONIAN. 

18,000  ft. 
Old  Red  Sandstone. 

SILURIAN. 
33,000  ft. 

CAMBRIAN. 
25,000  ft. 

Earliest  true  Reptiles. 

Earliest  Amphibian  (Labyrinthodont)  ;  extinc- 
tion of  Trilobites  ;  first  Cray-fish  ;  Beetles  ; 
Cockroaches;  Centipedes;  Spiders.  Luxu- 
riant land  Vegetation. 

Cartilaginous  and  Ganoid  Fishes  ;  earliest  land 
(snail)  and  freshwater  Shells;  Shell-Fish 
abundant;  decline  of  Trilobites;  May-flies; 
Centipedes  ;  Crab.  Land  Vegetation. 

Pearliest  Fish  ;  the  first  Air-Breathers  (Insects, 
Scorpions)  ;  Brachiopods  and  4-gilled  Cepha- 
lopods  (Nautiloids)  very  abundant;  Trilo- 
bites :  Corals  ;  Graptolites. 

Trilobites  ;  Brachiopod  Mollusks;  Corals  (rare). 

ARCH.EAN. 
35,000  ft. 
Huronian. 
Laurentian. 

No  undoubted  traces  of  fossils. 

PRIMEVAL.                    |  Non-sedimentary. 

156  THE  EARTH  AND  ITS   STORY. 

The  Variation  and  Extinction  of  Animal  Forms. - 
Just  what  it  is  that  causes  animal  forms  to  vary  and 
ultimately  to  develop  into  new  types  or  forms  wholly 
unlike  themselves,  is  not  always  apparent ;  but  probably 
in  most  cases  the  variation,  apart  from  an  inherent 
physiological  tendency  of  the  organism  to  vary  some- 
what in  its  form,  is  brought  about  through  a  number 
of  distinct  causes.  Among  these  may  be  enumerated 
changes  in  the  character  of  the  food-supply,  the  matter 
of  climate,  mechanical  impacts  resulting  from  accommo- 
dation to  immediate  environments,  special  necessities  of 
locomotion  and  movement,  and  so  forth.  Adaptation, 
or  fitting  to  all  these  requirements,  may  bring  about 
success  in  the  "struggle  for  existence,"  a  condition 
that  is  rendered  more  or  less  permanent  by  the  weeding 
out  or  extermination  of  such  forms,  or  groups  of  forms, 
as  have  not  been  able  to  accommodate  themselves  in 
habit  or  otherwise  to  the  necessities  of  their  ever- 
changing  surroundings.  This  process  of  natural  selec- 
tion is  largely  the  determining  element  which  brings 
about  evolution. 

It  is  commonly  believed  that  the  process  of  modifica- 
tion is  an  exceedingly  slow  one,  and  probably  in  most 
cases  this  is  so.  Hundreds  or  thousands  of  years  may 
be  required  to  impress  newly  acquired  characters  in  such 
a  way  as  to  render  them  (for  a  time)  permanent,  and 
thereby  to  create  new  species.  Yet  it  is  by  no  means 
certain  that  some  new  types  were  not  evolved  in  a  com- 
paratively short  period,  by  a  sort  of  saltus  or  jump; 
the  problem  is  snch  that  it  does  not  permit  of  easy 
solution,  although  it  is  certain  that  within  the  period  of 
man's  own  history  or  observation,  —  or  through  a  space 


FOSSILS  AND    THEIR    TEACHINGS.  157 

of  time  of  from  four  thousand  to  five  thousand  years. 
—  there  have  been  few  changes  of  magnitude  in  either 
the  animal  or  the  vegetable  world,  so  far  as  the  making 
of  new  types  is  concerned.  The  causes  that  bring 
about  extinction  are  necessarily  closely  bound  in  with 
those  that  relate  to  the  appearance  of  species ;  and  they, 
too,  are  not  easily  determinable  for  particular  cases. 
Thus,  it  is  not  made  clear  why  the  horse  on  the  Ameri- 
can continent  should  have  become  extinct  long  before 
the  advent  of  the  Europeans,  when  its  modern  succes- 
sor, so  absolutely  like  the  ancient  animal  whose  fossil- 
ized bones  are  scattered  through  various  rock  deposits, 
finds  in  the  same  region  a  seemingly  congenial  home. 
Certain  conditions  doubtless  existed  which  were  destruc- 
tive to  equine  development  at  the  time,  or  at  least  not 
favorable  to  it. 

It  seems  to  be  a  well-established  fact  that  few  forms 
of  life,  or  the  groups  which  they  represent,  after  they 
once  disappeared  from  existence,  —  or  became  "  ex- 
tinct," as  geologists  say,  —  ever  again  reappeared  as 
constituents  of  a  new  fauna  or  flora.  Hence,  disap- 
pearances (as  well  as  appearances)  are  landmarks  in 
the  fixing  of  geological  chronology;  by  reading  much 
the  same  history  in  all  parts  of  the  globe  we  are  able 
to  locate  definitely  the  "  horizons  "  or  times  which  are 
made  typical  by  the  presence  or  absence  of  certain  ani- 
mal or  vegetable  types.  Thus  we  know,  referring  back 
to  the  table  on  page  155,  that  no  trilobites  are  found  in 
deposits  newer  than  the  Carboniferous ;  any  rock,  there- 
fore, that  contains  the  remains  of  these  animals,  belongs 
to  a  period  that  is  either  Carboniferous,  or  of  still  older 
date.  Again,  a  special  genus  of  trilobites,  known  as 


158  THE  EARTH  AND  ITS  STORY. 

Paradoxides,  has  never  yet  been  found  in  formations 
other  than  the  Cambrian;  hence,  it  is  typical  of  .the 
rocks  of  that  period,  and  eminently  serves  to  charac- 
terize them.  Paradoxides  is  a  "leading"  or  "type 
fossil,"  inasmuch  as  it  serves  by  itself  to  distinguish  a 
rock-formation.  Almost  every  species  of  fossil  has 
a  definite  position  in  the  geological  scale,  and  would 
by  itself  serve  to  locate  a  formation ;  but  oftentimes 
the  determination  of  species,  owing  to  insufficiency  of 
knowledge  or  the  obliteration  of  characters,  is  a  most 
difficult  task,  and  then  recourse  is  had  to  the  aspect  of 
the  entire  group  of  fossils  which  a  given  rock-mass  con- 
tains. This  generally  gives  the  age  or  position  without 
difficulty. 

Kinds  of  Fossils ;  Marine,  Terrestrial,  and  Fresh- 
Water.  —  Fossils  are  generally  divided  into  three 
classes,  —  land,  fresh- water,  and  marine,  —  being  the  re- 
mains of  animal  forms  which  lived  respectively  on  the 
land-surface,  in  the  streams  and  lakes  of  land-areas,  and 
in  the  waters  of  the  ocean.  It  is  manifestly  of  the  first 
importance  to  ascertain  to  which  of  these  classes  any 
given  association  belongs ;  as  this  will  determine  the 
kind  of  formation  of  which  it  constitutes  a  part — - 
whether  the  formation  is  of  terrestrial  origin,  a  lake 
or  river  deposit,  or  the  sediment  of  the  ocean.  Only 
after  knowing  this  are  the  physiographical  conditions 
surrounding  a  formation  made  clear  to  us.  Under 
the  name  of  "  brackish- water  fossils "  are  included 
those  forms  which  inhabited  a  mixture  of  salt  and 
fresh  waters ;  such  brackish  waters  are  found  in  the 
estuaries  or  lower  courses  of  all  large  streams  that 
discharge  directly  into  the  sea.  Many  interior  waters 


FOSSILS  AND   THEIR    TEACHINGS.  159 

have  become  brackish  or  salty  through  over-accumu- 
lation of  salt  in  their  basins;  an  accumulation  that 
may  have  been  brought  about  by  the  disappearance  of 
a  natural  outlet,  or  by  unusually  rapid  desiccation,  or 
by  a  combination  of  both  conditions.  The  Great  Salt 
Lake  of  Utah  is  an  example  of  a  fresh-water  lake 
turned  into  a  salty  one,  with  an  accommodation  of  its 
very  limited  fauna  to  brackish  water  conditions.  On 
the  other  hand,  it  is  equally  certain  that  from  what 
were  at  one  time  salt  or  brackish  interior  seas,  fresh 
waters  have  been  developed,  and  with  them  have  origi- 
nated certain  types  of  fresh-water  faunas.  The  possi- 
bilities of  such  conditions  must  always  be  present  in 
the  mind  of  the  geologist  when  making  his  explora- 
tions. 

The  Origin  of  the  Different  Kinds  of  Faunas.  —  The 
oldest  rock  formations  contain  the  remains  of  only  such 
animals  as  by  a  combination  of  their  characters  are 
thought  to  have  inhabited  the  sea.  This  circumstance 
has  led  to  the  very  just  conclusion  that  the  animals 
first  to  come  into  existence  were  of  an  oceanic  type. 
Fresh-water  and  land  animals  followed  these  consider- 
ably later.  Many  interesting  suggestions  have  been 
made  with  regard  to  these  later-appearing  faunas,  the 
method  of  their  origin,  etc.,  without  perhaps  yielding 
definite  or  positive  clews  concerning  their  relationship 
with  the  forms  that  inhabit  the  sea.  Yet  there  are 
good  reasons  for  assuming  that  the  faunas  of  fresh 
waters  are  merely  modifications  or  transformations  of 
oceanic  types,  becoming  such  through  gradual  accom- 
modation to  new  conditions  of  habitat  —  a  change  of 
location  from  the  oceanic  waters  to  those  of  the  inflow- 


160  THE  EARTH  AND  ITS   STORY. 

ing  streams.  Less  secure  is  the  ground  on  which  one 
seeks  to  explain  the  origin  of  the  dry-land  fauna,  as 
possibly  a  direct  transformation  from  both  the  fresh- 
water and  the  oceanic  faunas. 


SUCCESSION    OF   LIFE. 

Faunas  of  the  Early  Periods  (Paleozoic).  —  In  the 
oldest  of  what  are  generally  considered  to  be  sedimen- 
tary rocks,  the  Archaean,  no  unequivocal  evidences  of 
organic  life  have  yet  been  found,,  although,  doubtless, 
both  animal  and  vegetable  organisms  had  already  come 
into  existence  at  that  early  period.  The  life  of  the 
succeeding  Cambrian  period  was,  both  numerically  and 
in  the  variety  of  forms,  a  rich  one ;  but  the  types  repre- 
sented appear  to  have  belonged  exclusively  to  the  Li- 
ve rtebrata,  or  to  animals  wanting  a  vertebral  column. 
The  shellfish  (Mollusca)  and  crustaceans  (Trilobita) 
were  preeminently  abundant.  In  the  period  following, 
the  Silurian,  the  influence  of  the  Mollusca  was  still 
paramount, — hence  the  period  is  frequently  designated 
the  "  age  of  mollusks ; "  but  we  have  here,  in  addition, 
the  first  unequivocal  evidences,  in  the  shape  of  fish- 
spines,  teeth,  and  armor-plates,  of  the  existence  of  the 
higher  backboned  animals.  Here,  too,  belong  the  earli- 
est inhabitants  of  the  land  whose  remains  have  come 
down  to  us,  —  scorpions,  hemipters,  and  possibly  cock- 
roaches, true  air-breathers  of  the  modern  type.  The 
coral  animal,  whose  presence  in  the  Cambrian  deposits 
had  yet  hardly  been  detected,  seems  to  have  found  an 
unusually  congenial  home  in  the  seas  of  this  period. 
The  Devonian  was  preeminently  the  period  or  "age  of 


FOSSILS  AND   THEIR   TEACHINGS.  161 

fishes,9'  a  class  represented  by  the  two  familiar  types 
of  sharks  and  dog-fishes  (cartilaginous  fishes),  and  the 
nearly  related  ganoids,  the  last  comprising  forms  like 
the  modern  sturgeon  and  alligator-gar,  in  which  the 
body  was  protected  by  an  armor  of  enamel  plate  or 
scales.  The  more  highly  constituted  osseous  or  bony 
fishes  had  not  yet  been  evolved.  In  the  rocks  of  this 
period  we  find  the  earliest  traces  of  animals  that  in- 
habited fresh  water  (fresh-water  mussel),  and  the  first 
of  the  air-breathing  mollusks,  a  land  snail.  A  promis- 
ing terrestrial  vegetation  had  gradually  been  unfolding, 
which  in  the  succeeding  Carboniferous  age  attained  to 
almost  unparalleled  luxuriance.  The  vast  deposits  of 
coal,  which  have  so  long  administered  to  the  wants  of 
man,  bear  ample  testimony  to  this  enormous  develop- 
ment. For  the  first  time  we  here  meet  with  animal 
forms  of  a  grade  of  organization  higher  than  the  fishes, 
—  giant  animals  of  the  salamander  type,  and  known  as 
labyrinthodonts,  sporting  in  the  existing  carbonaceous 
marshes,  inhaling  an  atmosphere  possibly  surcharged 
with  carbon,  and  giving  forth  to  the  solitudes  not  im- 
probably the  earliest  organic  sounds  whose  audibility 
was  above  that  of  the  hum  of  insects.  Hitherto,  so  far 
as  the  facts  in  the  case  have  been  revealed  by  geology, 
a  general  silence  had  pervaded  the  organic  universe ; 
the  land,  as  well  as  the  water,  was  tenanted  by  organ- 
isms to  whom  the  production  of  sound  was  a  stranger, 
and  whose  conception  of  the  same,  if  such  conception 
actually  existed,  must  have  been  principally  dependent 
upon  the  interaction  of  the  inert  mechanical  forces 
alone.  The  Permian  period  brings  forth  the  earliest 
true  reptilian  forms,  —  forms  which  in  several  points  of 


162  THE  EARTH  AND   ITS   STORY. 

structure  foreshadowed  the  quadrupeds,  and  which  not 
unlikely  were  ancestral  to  them;  and  we  therein  note 
a  step  in  advance. 

Faunas  of  the  Middle  Periods  (Mesozoic) .  —  It  is  not 
until  the  succeeding,  or  Triassic,  period  that  we  meet 
with  the  first  of  that  series  of  animals,  the  Mammalia, 
whose  special  development  constitutes  the  most  marked 
feature  of  the  organic  life  of  the  present  day.  Lowly 
forms,  most  nearly  related  to  the  marsupials,  possibly 
usher  in  the  class  of  the  most  highly  organized  of  all 
animals.  With  this  period  a  distinctively  new  era 
dawns  upon  the  horizon.  The  familiar  types  of  the 
preceding  periods,  if  they  have  not  already  completely 
died  out,  now  rapidly  decline ;  new  forms  take  their 
place,  and  a  more  modern  aspect  is  gradually  intro- 
duced. The  mollusks  are  no  longer  for  the  most  part 
brachiopods,  but  of  the  type  of  the  snail  and  the  clam ; 
the  old-time  cuttle-fishes  of  the  four-gilled  order  (rep- 
resented in  our  day  by  the  nautilus),  although  still 
flourishing,  find  their  ultimate  successors  in  the  more 
highly  organized  two-gilled  squid-like  forms ;  the  horse- 
shoe and  ordinary  crabs,  and  their  allies,  have  usurped 
the  place  of  the  trilobite  among  crustaceans ;  while 
among  the  lower  orders,  such  as  the  sea-urchins  and 
polyps,  we  find  the  true  urchins  taking  the  place  of  the 
more  primitive  stone-lily  (crinoid),  and  the  star-coral 
that  of  the  tabulate  and  cup-coral  types.  Progressive 
development  is  everywhere  manifest;  we  proceed  from 
low  to  high,  from  the  more  generalized  to  the  more 
specialized.  The  distinction  in  the  faunal  aspect  sepa- 
rating the  Triassic  from  the  Permian  period  is  more 
marked  than  that  separating  any  other  two  consecutive 


FOSSILS  AND    THEIR    TEACHINGS.  163 

periods  since  the  Cambrian ;  we  recognize  here  a  great 
break,  a  seemingly  new  impetus  having  been  given  to 
the  peopling  of  the  earth.  Such  a  break  likewise  sepa- 
rates the  Cambrian  and  the  Archaean  periods.  The 
Jurassic  deposits  yield  the  earliest  unequivocal  traces 
of  a  feathered  creation,  although  seemingly  some  of  the 
fossil  foot-tracks  of  an  earlier  period  belong  to  birds ; 
reptilian  in  many  of  its  characters,  ornithic  in  others, 
the  first  of  the  feathered  tribe  (Archseopteryx)  with 
which  we  are  acquainted  is  a  reptile  as  well  as  a  bird. 
Its  contemporaries  numbered  many  of  the  most  bizarre 
forms  whose  records  have  been  left  to  us,  —  reptiles 
of  the  air,  sea,  and  land,  whose  ponderous  proportions 
are  in  many  cases  only  matched  by  the  whale,  and 
whose  avian  affinities  prove  them  to  have  been  the 
ancestral  stock  whence  some  of  our  modern  birds  have 
been  derived.  The  monsters  of  this  golden  "age  of 
reptiles "  were  largely  continued  into  the  succeeding 
Cretaceous  period,  when,  however,  they  gradually 
succumbed,  and  ultimately  completely  passed  away. 
Their  successors  are  the  turtles,  crocodiles,  lizards,  and 
serpents  of  the  present  day.  This  period  is  likewise 
marked  by  the  advent,  in  considerable  numbers,  of  the 
osseous  fishes,  the  type  of  fish-structure  which  domi- 
nates the  modern  seas. 

Faunas  of  the  Newer  Periods  (Cainozoic).  —  Passing 
from  the  Cretaceous  to  the  Tertiary  period,  we  note 
the  most  marked  of  the  numerous  organic  changes  that 
present  themselves  in  the  geological  system.  As  if 
with  one  jump,  the  shadows  of  existing  life  are  called 
upon  the  scene;  modern  type-structures  everywhere 
prevail,  even  though  generic  or  specific  identity  be  a 


164  THE  EARTH  AND   ITS   STORY. 

matter  of  later  times.  We  recognize  in  the  Tertiary 
fauna  the  type  of  the  existing  mammal,  bird,  reptile, 
amphibian,  and  fish ;  the  shells  are  essentially  of  the 
same  character  as  those  of  our  seas,  and  many  of  the 
forms  are  even  specifically  identical.  And  the  same 
may  be  said  of  the  starfishes,  sea-urchins,  and  polyps, 
down  to  the  lowest  order  of  animals  known.  Correla- 
tively  with  the  development  of  the  modern  fauna,  we 
remark  the  disappearance  of  those  singular  forms  which 
served  to  distinguish  the  preceding  periods,  —  the  sala- 
mandroids  of  the  Carboniferous  and  Triassic  periods, 
the  Jurassic  and  Cretaceous  bird-like  reptiles,  and  the 
toothed  birds  of  the  Cretaceous  period.  Finally,  in 
the  later  Tertiary  we  are  dealing  with  a  faunal  assem- 
blage practically  identical  with  that  of  the  present  day. 
Here  man  first  steps  in,  ruler  of  the  universe. 

The  periods  of  formation  that  we  have  been  consider- 
ing have  been  subdivided  by  geologists  into  minor 
periods  or  formations,  depending  upon  certain  special 
relationships  or  differences  ;  but  these  need  not  concern 
us  here.  They  have  also,  and  for  similar  reasons,  been 
united  into  more  comprehensive  groups,  defined  by  the 
big  breaks  that  have  already  been  indicated ;  but  these 
likewise  have  no  special  interest,  except  for  the  pur- 
poses of  classification. 


ORGANIZATION  OF  THE  LESS-KNOWN  FOSSILS.     165 


CHAPTER   XIV. 

THE     ORGANIZATION     OF    SOME     OF     THE    LESS-KNOWN 
GROUPS    OF    FOSSILS. 

Foraminifera.  —  The  animals  of  this  group  have  been 
described  in  the  chapter  dealing  with  Chalk  and  the 
Atlantic  Ooze  (pp.  27,  28).  As  fossils,  they  occur  in 
microscopic  forms  and  of  such  size  as  to  be  easily 
recognizable  by  the  eye ;  indeed,  some  of  the  elongated 
types,  as  Nodosaria,  Dentalina,  etc.,  measure  at  times 
a  third  of  an  inch  in  length  or  even  more.  Frequently 
the  shell  of  the  animal  has  been  completely  removed, 
and  we  have  then  only  the  filling,  or  the  "casts,"  of 
the  different  chambers  preserved.  This  is  largely  the 
case  with  the  Foraminifera  of  the  "  green  marls  "  of 
the  Atlantic  border  of  the  United  States,  where  we 
find  rounded  pellets  of  the  mineral  glauconite  repre- 
senting the  spaces  of  the  shells  which  were  at  one  time 
occupied  by  the  living  part  of  the  animal.  The  For- 
aminifera extend  back  in  geological  time  almost  to  the 
earliest  period,  and  they  show  a  remarkable  persistence 
in  their  general  forms.  Some  of  the  oldest  types  are 
barely  distinguishable  from  forms  living  at  the  present 
day.  Chalk  and  some  other  kinds  of  limestones  are 
made  up  in  large  part  of  the  shells  of  these  animals. 

Corals,  of  one  kind  or  another,  are  found  in  almost 
every  geological  formation ;  but  the  older  types  are 


166  THE  EARTH  AND   ITS   STORY. 

quite  distinct  in  structure  from  those  of  the  modern 
seas  and  of  the  more  recent  deposits.  And  possibly, 
when  we  speak  of  ancient  reef-structures,  we  are  not 
permitted  to  conclude  that  the  conditions  governing 
their  formation  were  the  same  as  those  which  govern 
reef-making  at  the  present  time,  either  as  to  tempera- 
ture or  depth  of  water.  The  older  corals,  from  the 
Cambrian  period  to  the  Carboniferous  inclusive,  are  of 
the  two  types  commonly  recognized  as  the  tabulate  and 
the  cup  corals.  In  both  of  these  types  the  partitions,  or 
septa,  which  in  the  recent  coral  radiate  off  from  a  cen- 
tral elevation  or  columella,  and  make  the  perfect  star 
that  is  so  well  known  to  all  who  have  looked  carefully 
at  a  complete  specimen,  hang  closely  to  the  sides  of 
the  individual  cups,  and  only  unite  with  one  another  at 
the  bottoms  of  the  cups.  Again,  in  both  the  tabulate 
and  cup  types,  the  coralla,  or  "calyces,"  are  partitioned 
off  by  a  number  of  distinct  horizontal  or  wavy  plates, 
which  are  the  tabulae.  In  the  first  of  these  groups  we 
have  compound  assemblages  of  cups,  or  coralla,  which 
are  often  united  in  the  form  of  chains  ("chain  coral," 
Halysites),  wasps'  nests  ("wasp-nest  coral,"  Michelinia)^ 
honeycombs  ("honeycomb  coral,". Favosites),  or  organ 
pipes  ("  organ-pipe  coral,"  Syringopora).  The  cup 
corals  are  usually  single,  and  can  be  easily  recognized 
by  their  elongated  or  depressed  cups  (Cyathophyllum, 
Heliophyllum,  ZapJirentis). 

Trilobites.  —  No  class  of  fossils  is  so  eagerly  sought 
after  by  the  young  geologist  as  the  trilobites.  Their 
singular  appearance,  so  suggestive  of  animals  of  a 
much  higher  grade  of  organization,  combined  frequently 
with  an  excellent  state  of  preservation,  is  what  perhaps 


ORGANIZATION  OF  THE  LESS-KNOWN  FOSSILS.    167 

makes  them  specially  attractive ;  at  any  rate,  a  trilobite 
hunt  is  always  a  selected  feature  in  the  study  of  paleon- 
tology. The  animals  of  this  class  are  all  extinct,  and 
have  been  so  since  the  close  of  the  Carboniferous  epoch ; 
hence,  they  are  a  distinctively  ancient  type.  The  name 
trilobite  ("  three-lobed "  animal)  is  based  upon  the 
fact  that  the  hard  part,  or  shell,  of  the  animal  is  in  most 
cases  divided  into  three  distinct  parts ;  an  anterior  part, 
or  head-shield  (which  protected  the  stomach  and  man- 
dibular  parts  placed  beneath  it),  a  tail-piece  (jiygidium), 
and  a  middle  piece,  or  abdomen.  In  many  of  the  forms 
the  shell  shows  an  additional  lateral  trilobation,  i.  e., 
a  right-hand  lobe,  a  middle  lobe,  and  a  left-hand  lobe ; 
but  the  name  is  not  derived  from  this  construction. 
On  top  of  the  head,  or  cephalic  shield,  we  usually  find 
a  central  eminence  or  swelling,  known  as  the  glabella ; 
and  it  is  immediately  beneath  this  that  it  is  assumed 
the  stomach  was  placed.  Two  compound  eyes,  fre- 
quently showing  well  their  many  facets,  and  at  times 
supported  on  long  stalks,  are  generally  found  lying  off 
the  sides  of  the  glabella.  The  abdominal  portion,  and 
less  often  the  tail-piece  of  the  animal,  are  divided  into 
a  number  of  distinct  segments ;  and  these  were  some- 
times so  freely  movable  upon  themselves  that  the 
animal  was  able  to  roll  itself  up  into  a  ball  (Phacops, 
Calymene),  in  the  manner  of  the  wood-louse  and  arma- 
dillo. Recent  discoveries  have  shown  conclusively  that 
the  living  animal  was  provided  with  filamentous  and 
gill-bearing  appendages  and  swimmerets,  much  like 
some  of  the  modern  shrimp-like  animals,  and  the  lim- 
ulus  or  horseshoe-crab.  Seemingly  the  trilobites  were 
more  nearly  related  to  the  latter  than  to  any  other 


168  THE  EARTH  AND  ITS   STORY. 

Animal  that  to-day  inhabits  the  sea.  They  were  true 
crustaceans,  and  all  of  them  marine  in  habit,  with  a 
leaning  to  shallow  and  muddy  waters.  They  were  of 
the  most  diverse  sizes,  ranging  from  forms  (^Agnostus) 
that  were  no  larger  than  the  head  of  a  pin,  to  others 
that  measured  a  foot  or  even  nearly  two  feet  in  length 
(Paradoxides,  Asaphus)  ;  and  it  is  singular  that  both 
the  largest  (or  very  nearly  the  largest)  and  the  smallest 
forms  occur  in  association,  and  in  nearly  the  oldest  of 
the  rock  formations.  (Plate  53,  Figs.  4,  4a  ;  Plate  54.) 
Crinoids  or  Stone-Lilies.  —  Next  after  the  trilobites, 
perhaps  the  best  known  of  the  fossil  forms  are  the 
crinoids,  or  stone-lilies.  They  are  animals  which  be- 
long near  to  the  starfishes,  of  which,  in  fact,  they 
have  by  some  naturalists  been  constituted  a  sub-class. 
The  relationship  between  the  two  groups  is  not  imme- 
diately apparent.  If  you  take  a  many-armed  starfish, 
turn  it  with  its  mouth  looking  upward,  and  gently  fold 
over  the  arms  into  a  bunch,  and  then  imagine  it  has 
a  long  stalk  to  support  it,  you  will  have,  in  all  essen- 
tial details,  a  crinoid ;  the  fact  is,  there  are  one  or  two 
forms  of  starfish  which  have  a  short  appendage  to 
their  backs,  and  this  appendage  is  by  many  considered 
to  be  the  remains  of  what  we  recognize  in  the  crinoid 
stem.  A  crinoid,  or  stone-lily,  in  its  completion  con- 
sists of  a  stony  body  or  calyx,  supported  on  a  long, 
many-jointed  stem,  which  stem  (either  cylindrical  or 
pentagonal  in  outline)  was  rooted  to  the  sea-bottom 
during  the  life  of  the  animal.  Within  the  calyx  were 
contained  the  soft  parts  of  the  animal,  with  a  central 
mouth  looking  upwards ;  or,  if  the  calyx  hung  over 
like  the  tulip-bell,  then  naturally  the  mouth  looked 


Plate  53. 


^^.-•- , 


l] 


FOSSILS. 

1,3.  Crinoids,  or  "stone  lilies."  1,  la.  Pentremites.  2.  2a.  Crinoid-stem  "buttons." 
3.  Crinoid  with  stem  attached.  5.  Glyptocrinus.  4.  Trilobite  (Calymene). 
4a.  The  same  rolled  up. 


Plate  54. 


FOSSILS.  —  TRILOBITES. 

1.  Homalonotus  (from  the  Devonian).  2.  Head  of  Pliacops,  showing  the  two  lentil- 
shaped  eyes.  3.  Phacops  (Silurian).  4.  Body  of  Homalonotus.  5.  Paradoxides, 
with  the  head  sheared  off  from  the  body  (Cambrian). 


ORGANIZATION  OF  THE  LESS-KNOWN  FOSSILS.   169 

downwards.  From  the  border  of  the  cup  sprung  five 
many-jointed  arms,  which  subdivided  at  short  intervals, 
and  on  their  inner  faces  carried  numerous  delicate, 
also  many-jointed,  feather-like  appendages  (or  pin- 
nules), whose  motion  doubtless  helped  to  bring  a  food- 
supply  to  the  animal,  and  perhaps  additionally  served  in 
the  process  of  respiration.  (Plate  53,  Figs.  1,  2,  3,  5.) 

The  parts  of  the  crinoids  that  are  usually  found  are 
the  segments  of  the  jointed  stem,  the  so-called  "cri- 
noid  buttons."  These  are  of  various  forms  and  sizes, 
ranging  upwards  to  an  inch  in  diameter;  but  they 
almost  invariably  show  one  character  in  common,  the 
central  hole  or  perforation.  Through  the  continuous 
hole,  from  one  end  of  the  stem  to  the  other,  passed 
a  ligament,  or  muscular  string  of  some  kind,  which 
helped  to  keep  the  different  parts  together.  Crinoid 
buttons  and  sections  of  stems  are  at  times  so  abundant 
as  virtually  to  build  up  a  "  crinoid  rock  "  or  reef,  and 
this  more  particularly  among  the  Carboniferous  depos- 
its. Stems  have  been  found  which  measured  three  or 
even  four  feet  in  length,  and  others  existed  which  were 
yet  much  larger.  The  group  is  an  ancient  one,  which 
attained  its  maximum  development  in  the  period  cov- 
ered by  the  Silurian,  Devonian,  and  Carboniferous 
formations ;  at  the  present  time  it  appears  to  be  ver- 
ging on  extinction,  almost  the  only  localities  where  its 
representatives  occur  in  abundance  being  the  Carib- 
bean and  West  Indian  Seas. 

Brachiopods.  —  Under  this  name,  and  generally  re- 
ferred to  the  class  of  mollusks,  although  perhaps  show- 
ing more  actual  affinity  with  certain  kinds  of  worms, 
are  grouped  an  association  of  shell-bearing  animals 


170  THE  EARTH  AND  ITS   STORY. 

which  are  of  the  first  importance  in  the  decipherment 
of  rock-formations.  They  are,  to  the  older  and  middle 
periods  of  geological  history,  what  the  ordinary  shell- 
fish, the  clams  and  snails,  are  to  the  more  modern 
rocks,  and  as  constituents  of  the  world's  existing  fauna. 
The  brachiopod  shell  was  always  a  double  one,  i.e.,  con- 
sisted of  two  valves;  but  it  differed  from  that  of  ordi- 
nary clams  or  bivalve  shell-fish,  in  that  the  two  valves 
were  of  unequal  size,  a  larger  and  a  smaller.  The  beak 
of  the  larger  valve  was  usually  perforated  at  its  centre ; 
and  through  this  aperture,  which  was  sometimes  situ- 
ated below  the  beak,  passed  an  attaching  muscular 
bundle  or  peduncle.  Another  feature  distinguishing 
the  brachiopod  shell  from  that  of  the  ordinary  shell- 
fish is  the  right  and  left  symmetry  of  each  individual 
valve;  a  line  drawn  downward  from  the  beak  divides 
the  shell  into  an  equal  right-hand  and  left-hand  part. 
This,  as  we  know,  is  not  the  case  with  the  clam  and 
its  allies,  where  the  beaks  are  usually  placed  consid- 
erably forward  (less  often  backward,  and  still  less 
frequently  central).  Of  course,  a  few  exceptions  to 
both  conditions  could  be  cited  from  either  class  of  or- 
ganisms. In  most  brachiopods,  there  was  contained 
within  the  soft  body  of  the  animal  a  limy  arm-skele- 
ton, or  internal  support,  known  as  the  " spiral"  and 
"  carriage-spring  arrangement,"  against  which  were 
appressed  the  delicate  and  freely  movable  arm-gills, 
constructions  which  are  not  present  with  the  true  mol- 
lusks.  The  shell  itself  is  generally  of  lime  construc- 
tion ;  but  in  exceptional  forms  it  is  of  a  horny  texture, 
which  has  served  in  some  instances  to  preserve  it  un- 
changed throughout  nearly  all  geological  time. 


Plate  55. 


FOSSILS. — TYPES   OF   BRACHIOPODS. 

1,  la.  lb.  Terebratula.  2.  Terebratella.  3,  3a.  Rhynchonella.  4. 4a.  Atrypa. 
5.  Athyris.  6.  Merista.  7.  Ketzia.  8.  Strophomena.  9.  9a.  9b.  Spirifer. 
10,  lOa.  Leptaena.  11.  Productus.  12,  12a.  12b.  Orthis.  13.  Chonetes. 


Plate  56. 


FOSSILS.  — TYPES  OF  CEPHALOPODS. 

1    Belemnites  (internal  shell  of  a  fossil  cuttle-fish,  squid,  or  calamary). 

2-5.  AMMONOIDS.-S.  Scaphites.      3.  Ancyloceras.     4.  Crioceras.      5.    Baculites. 

6-7.  NAUTILOIDS.— 6.  Nautilus.    7.    Orthoceras. 


ORGANIZATION   OF  THE  LESS-KNOWN  FOSSILS.    171 

The  Brachiopoda  are  surpassingly  abundant  in  nearly 
all  the  older  formations;  and  it  is,  perhaps,  not  wrong 
to  say  that  they  culminated  as  early  as  the  Silurian 
period.  Very  nearly  the  oldest  fossil  known  to  us, 
found  at  the  base  of  the  Cambrian  series  of  rocks,  is 
one  so  near  to  the  modern  lampshell  or  goose  brachio- 
pod,  the  Lingula,  that  for  many  years  it  was  considered 
to  be  all  but  specifically  identical ;  of  late  years  some 
special  characteristics  have  been  found  to  distinguish 
it,  and  it  is  now  known  as  Lingulella.  Another  very 
ancient  type,  and  still  living,  although  in  restricted 
numbers  in  the  modern  seas,  is  Discina.  The  genera 
Spirifer,  Orthis,  and  Rhynchonella  are  amongst  the 
most  abundant  of  the  Silurian  and  Devonian  fossils. 
An  abundant  form  of  the  Jurassic,  Cretaceous,  and 
Tertiary  deposits  is  Terebratula.  The  group  has  little 
importance  at  the  present  time,  having  been  almost 
entirely  superseded  by  the  true  mollusks  —  the  snails 
and  bivalves.  (Plate  55.) 

Ammonites  and  their  Allies.  —  These  are,  broadly 
speaking,  ancient  cuttle-fishes,  which  inhabited  shells 
of  various  forms  and  sizes,  — some  of  them  the  largest 
of  all  known  shells  —  and  whose  only  near  modern 
representative  is  the  beautiful  pearly  nautilus.  This 
animal,  as  is  well  known,  inhabits  a  chambered  shell, 
almost  all  of  it  being  located  in  the  anterior  chamber, 
while  the  posterior  series,  with  their  partitioning 
"septa,"  appear  to  serve  mainly  as  a  helping  float. 
Through  the  different  septa,  nearly  in  the  centre  of 
each,  passed  a  tube  or  siphuncle,  in  which  was  located 
the  attaching  muscle  of  the  animal ;  this  siphuncle  dis- 
appears with  decay,  and  in  its  place  we  have  merely 


172  THE  EARTH  AND  ITS   STORY. 

the  central  perforations  of  the  septa.  All  of  the  type 
of  cuttle-fishes  that  conform  within  close  limits  to  the 
nautilus  are  known  as  "nautiloids,"  but  they  differ 
from  one  another  in  the  manner  of  the  winding  of  the 
shell.  Thus,  in  the  Silurian  G-yroceras,  the  shell  winds 
up  in  an  open,  instead  of  a  closed,  coil;  in  Lituites  it 
is  partly  coiled,  while  a  portion,  that  which  finally 
accommodates  the  body,  was  thrown  off  in  a  straight 
tangent  to  the  initial  coil ;  in  the  Cambrian  Cyrtocera*, 
we  have  nearly  a  curved  union  of  chambers,  looking 
like  an  antelope's  horn ;  and  finally,  in  Orthoceras, 
which  after  the  nautilus  itself  is  the  most  abundant  of 
the  known  forms,  the  shell  is  perfectly  straight.  De- 
spite these  variations,  the  characters  which  they  have 
in  common  serve  to  unite  them  as  nautiloids. 

Closely  related  to  the  nautiloids,  and  in  a  measure 
running  parallel  with  them  in  the  diversity  of  their 
forms,  are  the  "ammonoids,"  whose  most  distinctive 
type  is  the  Ammonites  (" Jupiter-Ammon  Stone").  In 
this  form,  and  equally  so  in  its  allies,  the  shell  is 
much  as  in  the  nautiloids  ;  but  the  septa,  instead  of 
being  simple  in  construction  as  they  are  in  the  nauti- 
lus, are  complicated  by  a  series  of  remarkable  infold- 
ings,  the  extent  of  which  can  be  seen  by  examining  the 
lines  of  "  suture "  where  the  septa  come  to  the  out- 
side of  the  shell.  They  give  a  peculiarly  ornamental 
appearance  to  the  surface,  very  different  from  anything 
that  is  to  be  found  on  the  shell  of  the  nautiloids.  We 
speak  of  the  septal  marks,  or  sutures,  as  "foliated," 
instead  of  "undulated,"  as  they  are  in  Nautilus,  Or- 
thoceras,  etc.  Another  difference  separating  the  two 
groups  is  found  in  the  position  of  the  siphuncle,  which 


ORGANIZATION  OF  THE  LESS-KNOWN  FOSSILS.    173 

in  the  ammonoids  runs  to  one  side  (on  the  back,  or  dor- 
sally)  of  the  different  chambers.  All  the  ammonoids 
are  extinct  at  the  present  day,  and  have  been  so  since 
the  beginning  of  the  Tertiary  period ;  nor  do  we  know 
of  any  forms  which  preceded  the  Carboniferous  period, 
except  a  limited  number  of  types  {G-oniatites,  Cly- 
menia)  which  seemingly  united  them  with  the  nauti- 
loids.  Not  knowing  the  soft  parts  of  the  animal, 
naturalists  have  not  been  able  positively  to  determine 
its  relationships ;  and  perhaps  a  broader  difference  sep- 
arates it  from  the  nautiloids  than  is  generally  admitted. 
Some  authors  have  indeed  gone  so  far  as  to  assume 
that  the  ammonoid  shell  was  internal,  and  not  external, 
more  like  what  we  find  in  the  modern  Spirula,  the 
pearly  shells  of  which  are  so  abundantly  thrown  up 
on  portions  of  our  Eastern  coast.  (Plate  52.) 

The  shell  of  the  ammonoids  shows  the  same  varia- 
tions in  coiling,  etc.,  that  are  found  among  the  nauti- 
loids. It  is  closely  coiled  in  Ammonites,  coiled  in  an 
open  plane  in  Crioceras,  partially  coiled  in  Ancyloceras, 
doubly  incoiled  in  Scaphites,  merely  curved  in  Toxo- 
ceras,  coiled  in  an  elevated  spire  in  Turrilites,  and 
finally  it  is  perfectly  straight  in  Baculites.  Most  of 
these  departures  appear  toward  the  close  of  existence 
of  the  group  (Jurassic,  Cretaceous)  ;  and  it  is  sur- 
prising as  reversing  the  order  of  appearance  among 
the  nautiloids,  where  the  less-coiled  forms  come  first, 
and  are  then  followed  by  the  uncoiled  and  the  straight 
shells.  (Plate  56.) 

Belemnites.  —  Under  this  name  geologists  recognize 
a  type  of  fossil  which  represents  the  modern  squids 
or  calamaries  of  the  regular  ten-armed  tribe  of  cuttle- 


174  THE  EARTH  AND  ITS   STORY. 

fishes,  in  which  whatever  represents  the  shell  is  inter- 
nal, and  not  external.  This  shell,  so-called,  is  familiar 
to  many  readers  under  the  form  of  the  horny  "pen" 
of  the  loligo,  and  of  the  limy  "  cuttle-bone  "  which 
so  often  finds  a  place  in  the  cage  of  canary  birds.  In 
the  belemnites,  or  belemnoids,  the  correspondent  of 
this  shell  was  a  cylindrical  object,  oftentimes  having 
the  appearance  of  a  cigar  (hence  "fossil  cigars"),  with 
an  expansion  in  front,  and  containing  a  small  cham- 
bered cone  in  the  upper  part  of  its  central  cavity.  It 
seems  that  to  the  top  of  this  cone  was  fitted  the  base 
of  the  "  ink-bag,"  the  organ  from  which,  as  in  the 
living  squids,  an  inky  fluid  was  projected  at  the  will 
of  the  animal.  Enough  of  the  soft  parts  of  the  belem- 
nite  has  been  preserved  clearly  to  establish  the  relation- 
ship of  the  animal,  and  to  give  it  its  proper  position 
beside  its  modern  ally.  The  belemnite  shell,  which  is 
the  only  portion  of  the  animal  that  is  usually  preserved 
in  its  fossil  form,  may  measure  several  inches  in  length, 
and  not  infrequently  it  exceeds  a  foot.  It  occurs  in 
particular  abundance  in  the  Jurassic  and  Cretaceous 
rocks,  and  seems  to  entirely  disappear  with  the  latter. 
A  most  interesting  circumstance  connected  with  the 
fossilization  of  these  animals  is  the  preservation  of  the 
solidified  ink.  This  "  fossil  sepia,"  for  that  is  what 
it  really  is,  has  under  proper  treatment  been  made 
to  yield  good  writing  and  painting  fluid  —  a  prepa- 
ration extending  back  hundreds  of  thousands,  or  even 
millions,  of  years.  (Plate  56,  Fig.  1.) 


FOSSIL   FISHES,   BIRDS,   AND   HEP  TILES.        175 


CHAPTER    XV. 

FOSSIL  FISHES,    BIRDS,    REPTILES,    AND    QUADRUPEDS. 

Fossil  Fishes.  —  The  earliest  positive  evidences  that 
we  have  of  the  appearance  of  fishes  are  found  in  a  few 
fragmental  parts  (teeth,  spines,  and  plates)  of  the 
newer  Silurian  period.  These,  as  well  as  those  of  the 
succeeding  periods  up  to  the  Jurassic,  belong  almost 
exclusively  to  the  group  of  cartilaginous  fishes,  like 
the  shark,  ray,  etc.,  in  which  the  backbone  has  not  yet 
been  completely  converted  into  bone  ;  and  to  a  second 
group,  —  not  distantly  removed  from  these,  —  the  mem- 
bers of  which  are  commonly  spoken  of  as  ganoids.  A 
common  character  of  the  latter  is  the  armature  of  large 
or  small  enamel  (or  bony)  plates,  which  formed  an  al- 
most complete  casing  to  the  animal ;  hence,  these  fishes 
are  frequently  spoken  of  as  "armored"  and  "bucklered" 
fishes,  among  which,  as  lingering  modern  representa- 
tives, are  the  sturgeon  and  the  alligator-gar.  The 
ganoids  are  so  abundant  in  the  rocks  of  the  Devonian 
period  that  this  time-measure  is  often  styled  the  "  age 
of  fishes."  Among  the  largely  armored  forms  may  be 
mentioned  Ceplialaspis,  Pteraspis,  Pterichthys,  which 
have  of  their  kind  no  existing  representative;  Holop- 
tychius  appears  to  have  been  nearly  related  to  the 
sturgeon.  The  gigantic  Dinichthys  and  Titanichthys, 
measuring  perhaps  twenty  feet  or  more  in  length,  and 


176  THE  EARTH  AND   ITS   STORY. 

likewise  from  the  Devonian  rocks,  were  seemingly  near 
allies  of  the  modern  lung-fishes,  and  indicate  a  passage 
to  the  next  higher  group  of  animals,  the  amphibians, 
which  appear  for  the  first  time  in  the  formation  im- 
mediately following.  The  type  of  the  modern  bony 
fishes,  such  as  the  herring,  carp,  salmon,  etc.,  acquires 
no  prominence  before  the  Cretaceous  period ;  and  even 
then  the  remains  that  have  been  found  hardly  prepare 
one  for  the  varied  fish-fauna  which  so  largely  appears 
in  the  lower  Tertiary  series  of  rocks. 

Reptiles.  —  The  earliest  known  reptiles  occur  in  the 
rocks  of  the  Permian  period;  but  it  is  not  until  we 
reach  the  later  Triassic,  and  especially  the  Jurassic, 
deposits,  that  we  find  a  broad  diversity  of  type-struc- 
ture represented.  Much  of  this  time-period  is,  in  fact, 
known  as  the  uage  of  reptiles."  Among  the  more 
prominent  of  the  Jurassic  forms  were  the  free-swim- 
ming, oceanic  Ichthyosaurus,  Plesiosaurus,  and  Pliosau- 
rus,  whose  anterior  and  posterior  limbs  were  incased  in 
skin  or  integument,  and  converted  into  true  paddling 
organs.  Some  of  these  "  oceanic  crocodilia,"  as  they 
have  been  sometimes  called,  measured  as  much  as 
twenty  or  thirty  feet  in  length.  Another  group  of 
reptiles  of  this  period,  which  acquired  further  develop- 
ment in  the  succeeding  Cretaceous  epoch,  and  to  which 
special  significance  attaches  because  by  many  zoolo- 
gists they  have  been  assumed  to  represent  a  type  that 
was  ancestral  to  certain  forms  of  birds,  is  the  Dinosau- 
ria  ("  terrible  reptiles  "),  bizarre  monsters  in  principal 
part,  which  combined  in  a  wonderful  manner  the  char- 
acters of  both  birds  and  reptiles.  c*$ome  of  the  types  of 
this  group  —  such  as  Stegosaurus,  Brontosaurus,  Came- 


2. 

FOSSILS. 


1.  Archseopteryx,  a  reptile-like  bird  from  the  Jurassic  deposits  of  Bavaria  (specimen  in 

the  Berlin  Museum). 

2.  Rhamphorhynchus,  a  Aringed  reptile  or  Pterodactyl  from    the  Jurassic 

deposits  of  Bavaria  (specimen  in  Yale  Museum). 


Plate  58. 


1.  Plesiosaurus,  a  marine  swimming  reptile.     2.   Ichthyosaurus,  a  somewhat  related 
form;  both  of  them  are  largely  represented  in  the  Jurassic  rocks. 
3.   Clidastes,  a  sea-serpent  of  the  Cretaceous  period.      4.  5.   Toothed  birds 
(Odontornithes),  from  the  Cretaceous   rocks   of  America.     4.   Ichthyornis. 
6.  Hesperornis. 


FOSSIL   FISHES,   BIRDS,    AND  REPTILES.        177 

rasaurus,  Triceratops  —  ware  among  the  largest  of  all 
known  animals,  measuring  from  twenty  to  seventy 
(perhaps  ninety)  feet  in  length.  They  appear  to  have 
been  mainly  herbivorous  in  habit,  and  to  have  inhab- 
ited swampy  or  marshy  tracts.  A  certain  number 
of  dinosaurs,  like  Iguanodon  and  Hadrosaurus,  were 
erect  in  posture,  or  at  least  partially  so,  a  condition 
in  progression  to  which  their  greatly  elongated  hind 
appendages  well  fitted  them;  it  is  to  such  animals, 
doubtless,  that  many  or  most  of  the  large  three-toed 
impressions  that  are  found  in  certain  rock-deposits, 
and  had  for  a  long  time  been  referred  to  birds,  belong. 
None  of  the  animals  of  this  class  appear  to  have  sur- 
vived into  the  Tertiary  period.  (Plates  58,  59.) 

Pterodactyls.  —  These  are  large  and  small  reptile- 
like  animals,  to  an  extent  having  the  structure  of  birds, 
which  were  provided  with  a  great  tegumentary  expan- 
sion, in  the  nature  of  a  wing,  uniting  the  anterior  with 
the  posterior  limbs.  The  wing  is  mainly  supported  by 
a  greatly  elongated  fifth  finger  of  the  hand,  and  in  this 
respect  differs  entirely  from  the  representative  organ 
found  in  birds  and  bats.  Both  lower  and  upper  man- 
dibles were  in  some  of  the  forms  provided  with  croc- 
odilian teeth  —  teeth  implanted  in  distinct  alveolar 
sockets.  All  the  animals  of  this  group  are  confined 
to  the  Jurassic  and  Cretaceous  deposits ;  while  some 
forms  were  no  larger  than  a  pigeon,  others  (^Pterano- 
dori)  appear  to  have  measured  fully  twenty  feet  in 
expanse  of  wings.  (Plate  57,  Fig.  2.) 

Archaeopteryx.  —  This  singular  organism,  of  which 
only  two  specimens  showing  any  degree  of  perfection 
have  been  found,  —  one  now  in  the  British  Museum, 


178  THE  EARTH  AND  ITS   STORY. 

and  the  other  in  the  Museum  of  Berlin,  —  is  almost 
directly  intermediate  in  structure  between  bird  and 
reptile.  The  animal,  which  was  of  about  the  size  of  a 
crow,  had  a  bird-like  head  (yet  with  distinct  teeth  near 
the  extremities  of  the  beak),  bird-like  limbs,  true  feath- 
ered wings,  and  a  feathered  tail.  The  arrangement  of 
the  feathers  on  the  tail,  running  as  they  do  in  opposite 
series  on  the  two  sides  of  the  axis,  instead  of  radiating 
off  fan-like  from  an  abbreviated  extremity,  is  wholly 
unlike  what  is  to  be  found  in  any  true  bird,  while  the 
long  caudal  column  is  of  a  clearly  reptilian  character. 
The  body  portion  of  the  animal,  singularly  enough, 
appears  to  have  been  entirely,  or  almost  entirely,  naked, 
thereby  again  differing  from  birds.  The  two  specimens 
of  Archseopteryx  referred  to,  and  two  additional  feathers 
—  all  that  has  thus  far  been  found  of  the  animal  —  are 
from  the  Solenhofen  (Bavarian)  quarries  of  lithographic 
stone,  of  Jurassic  age.  (Plate  57,  Fig.  1.) 

Birds.  —  Remains  of  birds  are  not  abundant,  a  cir- 
cumstance which,  doubtless,  stands  in  association  with 
their  aerial  method  of  life.  The  oldest  fragmental 
parts  belong  to  the  Jurassic  rocks ;  but  almost  certainly 
some  of  the  smaller  three-toed  impressions  which  are 
found  in  more  or  less  abundance  in  the  sandstones  of 
the  Trias  are  the  foot-marks  of  these  animals.  It  is 
mainly  in  the  rocks  of  the  Tertiary  period  that  their 
fossils  acquire  any  significance,  and  even  there  they  are 
not  of  sufficient  abundance  or  importance  to  constitute 
them  sign-posts  in  the  procession  of  life.  A  number 
of  remarkable  giant  birds  (Dinornis,  Notornis),  having 
some  of  the  characters  of  the  modern  struthians  (os- 
triches and  their  allies),  but  much  more  powerful  in 


FOSSIL   FISHES,   BIRDS,   AND  REPTILES.        179 

their  frame,  are  known  from  comparatively  recent 
deposits  of  New  Zealand,  and  some  of  them  appear 
to  have  become  extinct  so  recently  as  to  be  hardly  be- 
yond the  memory  of  man.  Of  about  the  same  period 
is  the  JEpyornis  of  Madagascar. 

In  the  Cretaceous  of  the  Western  United  States  are 
found  the  remains  of  a  very  remarkable  group  of  birds, 
whose  whole  structure  was  absolutely  bird-like,  except 
in  the  one  character  of  having  a  full  series  of  socket- 
teeth  implanted  in  both  the  lower  and  upper  mandibles. 
These  constitute  the  Odontornithes,  or  "  toothed  birds," 
the  best  known  representatives  of  which  are  Hesper- 
ornis  regalis  and  Ichthyornis  dispar.  (Plate  58,  Figs. 
4,5.)  ' 

Mammalia  (Quadrupeds).  —  The  rocks  of  the  Ter- 
tiary period  are  preeminently  characterized  by  the  re- 
mains in  abundance  of  the  highest  of  the  animal  forms, 
the  Mammalia.  They  are  by  no  means  found  in  all 
classes  of  deposits  belonging  to  this  period,  since  most 
of  them  are  of  marine  origin;  but  here  and  there,  in 
old  lake-deposits,  in  ancient  river-beds,  in  caves,  and 
in  dried-up  bogs  and  swamps,  they  are  numerous,  and 
so  varied  in  the  multiplicity  of  their  types  that  this 
period  has  frequently  been  designated  the  uage  of 
mammals."  In  rocks  more  ancient  than  the  Creta- 
ceous, the  mammalian  remains,  such  as  they  are,  few 
and  fragmentary,  are  indicative  of  a  type  more  nearly 
marsupial  in  character  than  anything  else,  and  appar- 
ently related  to  the  lowly  forms,  kangaroo-rats,  etc., 
which  to-day  constitute  the  Australian  fauna.  The 
oldest  known  forms  are  perhaps  Dromatherium  and 
Microkstes,  both  of  them  from  the  Trias, 


180  THE  EARTH  AND  ITS   STORY. 

In  the  history  of  no  other  group  of  organisms  do  we 
find  a  more  distinctly  marked  progression  in  develop- 
ment than  is  furnished  by  the  Tertiary  quadrupeds. 
The  complete  chain  of  structural  modifications  which 
certain  groups  present,  and  the  steady  and  growing 
approximation  of  the  unfolding  fauna  to  the  fauna  of 
our  day,  constitute,  perhaps,  the  most  convincing  dem- 
onstration of  organic  evolution.  About  one-half  of 
all  the  existing  orders  of  quadrupeds  are  represented 
in  the  first  stage  of  the  Tertiary  period  (Eocene)  ; 
these  are  the  marsupials,  insectivores,  rodents,  whales, 
hoofed  animals  (ungulates),  bats,  lemurs,  and  possibly 
monkeys.  In  addition  to  these,  there  are  a  number  of 
orders  which  have  no  living  representatives  at  the  pres- 
ent time ;  among  such  may  be  mentioned  the  Anibly- 
poda,  which  perhaps  stood  not  far  in  their  relationships 
from  the  elephants,  and  comprised,  among  other  forms, 
ponderous  tusked  animals  {Dinoceras  or  Uintatheriutii), 
which  rivalled  the  elephant  in  proportions  ;  the  Creo- 
donta,  or  primitive  carnivores ;  and  the  Condylartkra, 
or  primitive  hoofed  animals.  (Plates  60,  61,  62.) 

In  the  middle  Tertiary,  or  Miocene,  we  find  repre- 
sentatives of  the  additional  orders  of  edentates,  or 
toothless  animals,  true  carnivores,  sirenians  (dugongs), 
elephants,  and  monkeys ;  and  among  actual  forms  of 
to-day  (although  the  exact  species  may  be  different), 
there  are  the  hedgehog,  mole,  porcupine,  beaver,  squir- 
rel, rabbit,  tapir,  rhinoceros,  hippopotamus,  hog,  deer, 
giraffe,  elephant,  cat,  dog,  and  hyena.  In  the  older 
(Eocene)  period,  the  bats  are  seemingly  the  only  im- 
mediate representatives  of  the  modern  fauna.  In  the 
upper  Tertiary,  or  Pliocene,  there  is  a  still  further 


Plate  59. 


FOSSIL  REPTILES  FROM  THE  WESTERN  UNITED  STATES. 

1.  Stegosaurus,  from  the  Jurassic  deposits. 

2.  Brontosaurus  (Jurassic). 

3.  Triceratops  (Cretaceous). 

(Restorations  by  Prof.  Marsh.) 


Plate  60. 


ANCESTRAL  FORMS  OF  THE  HORSE  (mainly  after  Marsh  and  Cope). 

1.  Phenacodvs,  earliest  form,  from  the  Eocene  of  Europe  and  America.  2.  Hipparion 
(Pliocene  and  newer  Miocene).  3.  Paleotherium  (Eocene  of  Europe). 
4.  Recent  two-toed  horse.  5.  Skull  of  Paleotherium.  6.  Skull  of  livimr 
horse.  7.  Successive  forms  of  the  American  horse-type,  as  illustrated  by  tl  <• 
structure  of  the  feet  and  teeth.  8.  Stages  in  the  development  of  the  European 
horse,  from  Paleotherium  (on  the  left),  through  Anchitheriuin  and  Hipparion, 
to  Equus  (modern). 


FOSSIL  FISHES,   BIRDS,   AND  REPTILES.        181 

approach  to  the  fauna  of  to-day  in  the  introduction  of 
an  additional  number  of  existing  types,  such  as  the 
sheep,  goat,  and  ox,  the  bear  and  camel,  and  among 
monkeys,  the  macaque.  Indeed,  the  greater  number 
of  the  genera  are  identical  with  the  genera  of  to-day, 
and  even  a  limited  number  of  living  species  appear  for 
the  first  time.  One  of  these  is  the  common  hippopota- 
mus, which  consequently  represents  about  the  oldest 
type  of  existing  quadruped.  In  the  Post-Pliocene 
period,  the  correspondence  between  the  existing  and 
extinct  faunas  is  still  further  increased  through  the 
large  preponderance  of  recent  species.  On  the  border- 
line of  this  and  the  preceding  period  we  meet  with  the 
first  unequivocal  remains  of  man  himself. 

Origin  of  Existing  Faunas.  —  It  can  be  said,  in  a 
broad  way,  that  the  existing  fauna  of  any  given  region 
is  most  closely  related  to  the  fauna  whose  remains  are 
found  in  the  same  area,  in  deposits  immediately  pre- 
ceding in  age  those  of  the  present  era.  The  North 
American,  European,  and  Asiatic  faunas,  for  example, 
are  strictly  a  development  from  the  Post-Pliocene 
faunas  of  approximately  the  same  regions ;  the  remark- 
able edentate  fauna  of  modern  South  America  —  the 
sloths,  armadillos,  and  ant-eaters  —  is  foreshadowed  in 
the  giant  Grlyptodon,  Mylodon,  and  Megatherium,  and 
their  allies ;  and  similarly,  the  diverse  marsupial  fauna 
of  the  Australian  continent  is  represented  by  the  ex- 
tinct Diprotodon,  Thylacoleo,  etc.  Naturally,  a  part  of 
every  extensive  fauna  is  the  result  of  incoming  of  forms 
from  beyond  the  border ;  it  has  been  made  such  through 
immigration.  It  has  been  possible  in  a  few  instances  to 
trace  the  lines  of  migration  which  were  taken  by  cer- 


182  THE  EARTH  AND   ITS   STORY. 

tain  animal  groups,  since  it  is  known  that  they  appeared 
earlier  in  time  in  some  regions  than  in  others.  Thus 
the  elephants,  bears,  swine,  oxen,  sheep,  and  antelopes 
appear  earlier  in  the  Old  World  than  in  the  New,  and 
presumably  there  was  a  migration  of  these  animals  in 
the  direction  of  the  Western  Hemisphere ;  conversely, 
the  true  dogs  seem  to  have  been  first  developed  on  the 
American  continent,  and  then  to  have  made  their  way 
to  the  Old  World.  With  all,  however,  it  must  be  said 
that  our  knowledge  on  these  points  is  hardly  precise 
enough  to  permit  us  clearly  to  indicate  the  actual  lines 
of  migration.  (Plate  62 .) 

Ancestral  Forms  of  Animals.  —  The  close  study  of 
fossil  remains  has  permitted  the  tracing  back  of  a  num- 
ber of  our  existing  animals  through  their  own  lines  of 
descent  —  that  is  to  say,  to  early  forms  largely  unlike 
themselves,  from  which  they  were  by  the  slow  pro- 
cesses of  evolution  developed  into  their  present  form. 
This  reconstruction  of  "parental  lines"  has  been  done 
for  some  of  the  dogs,  bears,  and  cats,  for  certain  deer, 
the  camel  and  the  horse  etc.,  and  for  none  more  com- 
pletely than  the  horse.  Plate  60  illustrates  the  re- 
spective modifications,  seen  plainly  in  the  elimination 
or  modification  of  certain  elements  of  the  foot  and  leg, 
—  reduction  in  the  number  of  the  toes,  abortion  of  the 
splints,  etc., — which  bring  the  modern  horse,  through 
various  polydactyl  forms,  from  its  most  ancient  progeni- 
tor, the  full  five-toed  Phenacodus,  to  its  existing  shape. 
Phenacodus,  which  was  an  animal  hardly  larger  in  size 
than  a  fox,  belongs  to  the  base  of  the  Eocene  series  of 
deposits.  As  if  in  proof  of  this  serial  modification,  the 
common  horse  even  to-day  shows  a  tendency  to  poly- 


Plate  61. 


RESTORATIONS   OF  QUADRUPEDS  OF  THE  TERTIARY  PERIOD. 

1.  Mastodon  angustidens  (Miocene). 

2.  Uintatherium  (Eocene  of  the  Western  United  States). 

3-   Helladotherium,  a  giraffe-like  animal  from  the  Pliocene  of  Greece. 

4.  Anthracotherium,  a  hoofed  animal  from  the  Oligocene  of  Europe. 


OF  THE 

UNIVERSITY 

OF  ,/ 

-' 


Plate  62. 


FOSSILS  OF  THE   POST-PLIOCENE   PERIOD. 

1-3.    Giant  edentates.      1.    Panochtus  (glyptodon).      a.  Megatherium.      3.    Mylodon. 
4.  Skull  of  Machairodus  or  Smilodon,  a  sabre-toothed  cat. 


FOSSIL   FISHES,    BIRDS,   AND   REPTILES.        183 

dactylism;  and  instances  are  not  rare  where  two  (and 
less  often,  three)  more  or  less  functional  toes  appear 
on  the  animal,  the  indication  of  a  reversion  to  its  prim- 
itive or  ancestral  type. 

The  Age  of  Man  and  the  Mammoth.  —  It  has  been 
the  custom  with  some  geologists  to  speak  of  the  latest 
geological  period  as  the  "  age  of  man  and  the  mam- 
moth," implying  that  in  the  association  of  these  two 
organic  types  there  was  a  marked  characteristic  im- 
planted upon  the  faunal  chain  of  the  world.  This 
division  of  time  is,  however,  an  unnatural  one,  and 
one  that  is  not  made  a  unit  by  its  own  construction. 
The  oldest  remains  of  man  are  of  too  infrequent  occur- 
rence to  permit  of  a  positive  statement  as  to  his  an- 
tiquity; and  they  are,  moreover,  not  coexistent  in  full 
time  with  those  of  the  mammoth.  That  he  was  a  con- 
temporary of  the  great  elephant  is  established  beyond 
question,  and  it  is  about  equally  certain  that  he  lived 
with  the  other  great  proboscidean,  the  mastodon.  Both 
of  these  elephants  are  to-day  extinct,  the  mammoth  sur- 
viving until  so  recent  a  period  as  to  have  its  carcass 
(frozen  in  the  soil  of  Siberia)  preserved  with  the  flesh, 
skin,  and  hair  still  ensheathing  the  osseous  framework. 
The  mammoth  and  mastodon  inhabited  both  continents, 
the  remains  of  the  latter  extending  back  to  the  Mio- 
cene period. 

The  researches  of  late  years  make  it  almost  certain 
that  the  oldest  man  of  which  skeletal  traces  have  been 
found  represented  an  inferior  type  as  compared  with 
the  man  of  to-day.  A  limitation  of  brain  capacity,  de- 
pressed arch  of  the  skull,  and  strong  forward  develop- 
ment of  the  orbital  roof,  suggest  direct  relationship 


184  THE  EAETH  AND   ITS   STORY. 

with  the  higher  apes,  or  at  least  a  degree  of  develop- 
ment not  very  much  above  them.  This  is  indicated  in 
the  specimens  of  Neanderthal  (Germany),  Shipka  (Bo- 
hemia), and  Spy  (Belgium),  and  in  an  anomalous  erect 
organism  (Pithecanthropus')  recently  discovered  in  the 
late  Tertiary  deposits  of  Java,  and  by  some  classed  as 
man,  and  by  others  (with  probably  more  justice)  as  a 
connecting  form  between  man  and  the  ape. 


PART    II, 

PHYSIOGRAPHY    AND    ECONOMIC   GEOLOGY. 


CHAPTER    XVI. 

THE  PHYSIOGNOMY  OF  THE  LAND-SURFACE. 

Physiognomy  of  Continents.  —  It  is  a  common  teach- 
ing in  text-books  of  physical  geography  that  the  conti- 
nents have  a  generally  identical  structure,  being  built 
up  of  opposite  mountain  chains,  with  a  great  central 
depression  between  them,  and  adjoining  littoral  plains. 
Thus,  if  we  take  the  continent  of  North  America  as 
our  type,  we  find  (illustrated  by  the  region  of  the 
United  States)  the  lowland  plains  of  the  Atlantic  and 
Pacific  borders,  the  Appalachian  and  Rocky  Mountain 
systems  respectively  in  the  East  and  in  the  West,  and 
between  them  the  great  depressed  land  of  the  Missis- 
sippi basin,  which,  gently .  rising  eastward  to  the  wes- 
tern foot  of  the  Alleghanies,  and  westward  to  the 
eastern  foot  of  the  Rocky  Mountains,  attains  elevations 
of  1,500  and  6,000  feet.  This  form  of  construction  in 
a  measure  adjusts  itself  to  the  continent  of  South 
America,  somewhat  less  so  to  Asia,  and  not  at  all  to 
Europe,  Africa,  or  Australia.  In  Europe  the  main 
mountain  axes  are  disposed  largely  at  right  angles  to 

185 


186  THE  EAETH  AND  ITS  STORY. 

one  another  (Scandinavian  Alps,  Pyrenean-Alpine  sys- 
tem), and  the  depressed  plains  of  greatest  extent 
(North  Germany,  Russia)  are  not  caught  up  between 
them.  In  Asia,  lofty  mountain  chains  (Kuen-Lun, 
Thian-Shan,  Altai)  occupy  the  heart  of  the  continent ; 
and  in  Africa,  much  of  the  central  interior  is  a  lofty 
plateau  which  cannot  even  be  said  to  be  supported  by 
bounding  mountain  chains. 

About  the  only  points  of  unity  that  the  different 
continents  have  with  one  another  are  their  expansion 
on  the  northern  side,  contraction  toward  the  south, 
whether  of  the  main  mass  or  of  their  peninsular  parts, 
and  the  close  bordering  of  mountain  chains  to  present 
or  past  coastlines.  No  absolutely  satisfactory  explana- 
tion has  yet  been  given  for  the  first  characteristic ;  the 
second  finds  its  solution  in  the  fact  that  the  border- 
line of  continents  and  oceans  is  preeminently  a  line  of 
weakness  in  the  crust,  and  along  it  are,  or  were,  reared 
up  the  newly  forming  and  formed  mountains ;  or  any 
very  large  breakage  within  a  continent  itself,  resulting 
in  the  formation  of  an  interior  sea,  is  likely  to  result 
in  mountain-raising  along  its  borders.  This  condition 
we  have  seen  exemplified  in  the  Mediterranean  area, 
with  the  uplifting  of  the  Alps  and  their  continuations. 
Continents  expand  seaward  by  having  mountain  masses 
thrown  out  seaward;  they  retreat  from  the  sea  also 
with  the  formation  of  mountain  masses ;  but  these  are 
interior,  and  face  a  breakage  within  themselves.  Hence, 
the  relation  existing  between  mountain  lines  and  the 
lines  of  sea-shore. 

The  fact  that  a  number  of  mountain  chains  lie  con- 
siderably inland  from  the  sea  —  Altai,  Carpathians  — 


THE  PHYSIOGNOMY  OF  THE  LAND-SURFACE.     187 

is  no  indication  that  they  were  not  formed  at  or  near 
the  sea-border.  Since  their  upheaval,  new  land  has 
formed  on  the  outside,  either  through  a  recession  of 
the  sea  (or  upheaval  of  the  land),  or  through  a  down- 
wash  of  continental  sediment.  Of  such  semi-alluvial 
construction  is  much  of  the  bottom-land  which  acts  as 
a  base  to  the  Rocky  Mountains,  the  Alps,  and  the  Him- 
alayas, and  the  off-flow  of  the  Asiatic  Mountains  north- 
ward through  Siberia  and  eastward  through  China.  No 
mountain  chain  is  of  newer  date  than  much  of  the  land 
which  separates  it  from  the  nearest  ocean. 

The  continental  coast-lines  of  the  western  side  of 
America  and  of  the  eastern  side  of  Eurasia  are  largely 
determined  by,  or  stand  in  direct  relation  with,  the 
trend  of  a  main  mountain  system.  On  the  west  side 
of  Europe  and  the  east  side  of  America  this  is  much 
less  markedly  the  case ;  and  a  number  of  prominent 
mountain  backbones  traverse  the  trend  of  the  main 
coast,  and  abut  directly  upon  the  sea.  Such,  for  ex- 
ample, are  the  Pyrenees  and  the  mountains  of  Spain, 
and  the  ridges  which  in  sharp  and  prominent  lines 
traverse,  in  a  north-east  and  south-west  direction,  Scot- 
land, Newfoundland,  etc.,  and  define  for  them  those 
serrated  projections  into  the  sea  which  make  their 
ragged  fjord-shores.  Such  mountain-invaded  coast- 
lines, frequently  designated  Has-coasts,  indicate  break- 
ages ;  the  mountains  extended  farther  in  the  line  of 
their  trend,  and  have  disappeared  beneath  the  sea 
through  probably  successive  falls.  The  Pyrenees  and 
the  mountains  of  Spain  at  one  time  extended  far  ocean- 
ward,  and  the  ridges  of  Scotland  connected  with  the 
outer  ridge  of  the  Scandinavian  peninsula.  The  Ork- 


188  THE  EARTH  AND  ITS   STORY. 

neys,  Shetlands,  and  Lofotes  are  the  remnants  that 
attest  this  breakage. 

Physiognomy  of  Mountains.  —  In  their  exterior  dress 
mountains  present  themselves  in  a  multitude  of  forms, 
from  the  isolated  mount  and  the  parallel-trending  ridges 
to  a  most  complex  system  of  elevations.  Further,  they 
vary  from  forms  which,  like  the  major  part  of  the  Alle- 
ghanies,  have  a  uniformly  monotonous  or  undulating 
aspect,  to  those  in  which  ragged  and  serrated  summits, 
dominant  peaks,  and  beetling  cliffs  are  the  marked 
characteristics.  The  older  the  mountain  the  more  uni- 
form, gentle,  or  monotonous  is  likely  to  be  the  contour 
that  defines  it;  for  in  the  ages  of  its  existence  whatever 
sharp  features  may  have  been  incised  into  it  will  have 
become  blotted  out  through  the  never-ceasing  action  of 
erosion.  A  good  type  of  such  an  ancient  monotonous 
mountain  is  furnished  by  the  even-backed  Alleghanies 
and  the  Blue  Ridge,  in  which  the  "peak"  element  is 
largely  wanting.  The  newer  the  mountain,  on  the  other 
hand,  unless  it  be  too  new,  the  more  likely  are  discor- 
dant or  emphatic  features  to  be  determined.  The  work 
of  destruction  is  sufficiently  energetic  to  carve  out  dom- 
inant features,  while  the  length  of  time  has  not  been 
sufficient  to  efface  them.  In  the  Alps,  Rocky  Moun- 
tains, and  Himalayas  we  have  good  examples  of  such 
ragged  and  comparatively  new  mountains. 

It  is,  however,  an  error  to  assume  that  old  and  new 
forms  can  always  be  readity  distinguished  by  their 
types  of  contour.  The  ancient  White  Mountains  of 
New  Hampshire,  although  of  less  height,  are  as  rugged 
in  their  contours  as  perhaps  the  greater  portion  of  the 
Rocky  Mountains ;  and  among  the  old  mountains  of 


Plate  48. 


THE  PHYSIOGNOMY  OF  MOUNTAINS. 

1.  The  Aiguille  du  Dru,  Savoy,  France.     2.  The  Bee-Hive  Mountain,  Alberta,  Canada 
Two  mountains  of  very  distinct  types  of  contour. 


THE  PHYSIOGNOMY  OF  MOUNTAINS. 

1.  The  Wetterhorn,  Switzerland,  one  of  the  most  precipitous  mountain  faces  of  magni- 

tude in  the  world;  the  convolution  of  its  rock-masses  is  clearly  exhibited. 

2.  The  Book  Cliffs,  Utah,  near  the  Green  River—  the  terminal  wall  of  a  lofty  plateau 

mountain. 


THE  PHYSIOGNOMY  OF  THE  LAND-SURFACE.      189 

Norway  we  find  a  development  of  peaks,  needles,  and 
sharp  ridges  which  can  well  compare  with  some  of  the 
most  startling  effects  of  Alpine  scenery.     (Plates  48, 
49.) 

The  most  marked  structural  features  in  the  outer 
dress  of  a  mountain  are  the  steepness  of  rise,  the  divis- 
ion of  the  top-line  into  peaks  or  pinnacles,  and  the 
hollowing  out  of  the  slopes  into  gorges,  cloves,  basins, 
and  amphitheatres.  These  features  depend  upon  the 
positions  which  the  rock-masses  occupy  within  the  in- 
terior, and  the  work  of  destruction  and  denudation  on 
the  outside.  There  are  few  mountains  that  rise  with 
the  steep  slope  that  the  eye  ordinarily  pictures,  the 
deception  being  often  emphasized  by  from  20°  to  30°. 
When  a  mountain  is  assumed  to  rise  up  "  almost  verti- 
cally," the  actual  measurement  will  determine  the  slope 
to  be  probably  not  more  than  45°  or  50° ;  and  even  this 
is  an  uncommonly  severe  rise.  The  great  precipices 
themselves  rarely  exceed  for  their  full  height  60°  or 
65° ;  but  even  with  this  measure  they  would  appear 
to  the  observer  standing  in  front  of  them  very  nearly 
vertical,  and  under  certain  atmospheric  conditions  even 
to  overhang.  Such  an  appearance  is  presented  by  the 
giant  walls  of  the  Dolomites,  in  the  Tyrol,  and  by  that 
most  imposing  of  European  precipices,  the  7,000-foot 
wall  of  the  Wetterhorn  among  the  Swiss  Alps.  Of  less 
elevation,  but  with  greater  verticality,  are  the  moun- 
tain faces  which  bound  the  picturesquely  similar  valleys 
of  Lauterbrunnen  in  Switzerland,  and  the  Yosemite. 
The  most  precipitous  mountain  face  of  considerable 
elevation  in  the  Eastern  United  States  appears  to  be 
Wallface  Mountain,  in  the  Adirondacks,  fronting  the 


190  THE  EARTH  AND  ITS   STORY. 

celebrated  Indian  Pass.  Mountains  with  well-marked 
precipice  faces  usually  have  their  top  surfaces  gently 
falling  backward,  a  condition  that  suggests  for  many  of 
them  a  fault-upheaval  in  front. 

The  exaggeration  in  slope  that  appears  for  ordinary 
mountains  applies  equally  in  the  case  of  volcanoes.  It 
can  be  broadly  stated  that  the  "  sugar-cone  "  effects  to 
which  geographies  so  frequently  treat  us  do  not  exist. 
The  cones  of  such  lofty  volcanoes  as  Cotopaxi,  Popo- 
catepetl, Fusiyama,  etc.,  do  not  for  their  steepest 
parts  much  exceed  30°  to  35°,  and  for  their  greatest 
lengths  fall  considerably  below  this  measure.  Yet  even 
with  this  moderate  slope  the  mountains  are  wonder- 
fully imposing  in  their  presence.  The  slope  of  Etna  is 
reduced  to  12°  or  15°  ;  while  that  of  Mauna  Loa,  in 
Hawaii,  is  so  moderate — about  5°  to  7  —that  the 
mountain  aspect  is  almost  entirely  lost.  (Plate  36.) 

Peaks  of  real  magnitude  belong  properly  to  moun- 
tains of  comparatively  recent  construction,  but  in  the 
case  of  the  mountains  of  Norway  they  are  not  entirely 
absent  from  those  of  ancient  date.  They  rarely  rise 
even  in  their  exaggerated  types  more  than  a  few  thou- 
sand feet  above  the  crest-line  which  constitutes  the  true 
mountain- top,  and  it  cannot  be  positively  said  that  they 
ever  rose  much  higher ;  in  the  case  of  mountains  of  low 
elevation,  like  those  of  the  Appalachian  system,  they 
may  drop  to  a  thousand  feet  or  considerably  less, 
appearing  sometimes  as  mere  pimple  elevations  on  the 
general  mountain  backbone.  The  White  Mountains 
ridge  in  New  Hampshire,  of  which  Mt.  Washington  is 
the  central  figure,  has  some  eight  or  nine  peaks  (Adams, 
Madison,  Jefferson,  Monroe,  Jackson,  etc.)  rising  out 


THE  PHYSIOGNOMY  OF  THIS  LAND-SURFACE.     191 

of  it ;  but  their  elevations  are  retained  within  the  thou- 
sand feet  or  so  which  mark  the  interval  between  the 
general  height  of  the  ridge  and  the  top  of  its  most 
elevated  summit.  The  actual  peak-elevations  in  the 
Catskills,  although  the  mountains  are  themselves  of 
considerably  less  magnitude,  are  higher  than  in  the 
Presidential  Range,  rising  as  they  do  to  positions  of 
1,300  or  1,500  feet  above  a  general  plateau  elevation 
of  some  2,300  feet. 

The  loftiest  true  peaks  are  found  in  the  Himalaya 
and  Karakoram  Mountains,  where  there  is  an  actual 
elevation  above  the  crest  of  some  6,000  or  7,000  feet, 
and  exceptionally  perhaps  even  more.  Closely  follow- 
ing these  is  the  famous  Matterhorn  of  Switzerland, 
which  in  the  abruptness  of  its  demarkation  stands  pre- 
eminently as  the  type  of  what  is  frequently  designated 
"Alpine  peaks"  —  a  term  always  inappropriately  ap- 
plied to  the  peaks  or  summits  of  the  Appalachian 
mountains,  and  having  but  restricted  application  even 
in  the  case  of  the  Rocky  Mountains.  Pike's  Peak, 
with  an  absolute  elevation  of  14,147  feet,  rises  as  a 
mountain  8,000  feet  above  its  base  opposite  Colorado 
Springs ;  but  the  peak  itself  barely  exceeds  2,000  feet. 

In  this  consideration  no  account  has  been  taken  of 
volcanic  mountains,  whose  cones  are  frequently  spoken 
of  as  "peaks."  These  rise  as  individual  objects  consid- 
erably higher  than  the  true  mountain  peaks,  in  fact,  to 
nearly  twice  their  height.  Thus,  Ararat  has  a  clear 
sweep  of  about  13,000  feet,  Fusiyama  of  about  12,000 
feet,  and  Popocatepetl  (and  Orizaba)  of  10,000  feet 
above  the  surface  of  the  Mexican  plateau ;  the  last- 
named  presents  a  mountain  face  of  nearly  15,000  feet 


192  THE  EARTH  AND  ITS   STORY. 

to  the  bottom-land  from  which  it  sweeps  up  in  its  most 
graceful  form. 

The  true  mountain  peaks  depend  at  times  for  their 
existence  upon  rock-dislocations ;  i.e.,  they  have  been 
run  up  higher  than  the  crest  which  supports  them  by 
the  rocks  having  been  actually  forced  up  in  the  posi- 
tions which  they  now  occupy.  More  frequently,  per- 
haps, they  are  in  the  main  only  an  expression  of  the 
irregular  wear  of  the  mountain  mass,  standing  up  as  a 
relief  in  rock-resistance.  The  physiographic  features 
that  associate  themselves  with  mountain  peaks  and 
with  mountain  summits  generally,  cannot  all  be  re- 
ferred to  in  this  place,  but  a  few  of  those  best  known 
in  the  language  of  mountain  craft  are  the  following : 
The  Col  (Juch,  saddle,  or  yoke) :  the  crest  or  divide 
which  unites  two  mountain  peaks.  A  good  example 
of  such  col,  although  on  a  small  scale,  is  the  concave 
ridge  ("  saddle ")  which  unites  Mts.  Lafayette  and 
Lincoln  in  the  Franconia  Mountains.  Arete :  a  sharp 
ridge  of  rock  into  which  the  col  may  develop,  or  any 
similar  narrow  rock-wall  that  may  protrude  from  the 
mountain  face,  or  in  which  the  mountain  may  termi- 
nate. Some  of  the  aretes  are  so  sharply  cut  that  they 
can  be  readily  straddled.  Aiguilles  (needles)  :  the  ex- 
ceedingly sharp  pinnacles  into  which  a  mountain  crest 
may  be  worn,  a  structure  beautifully  shown  in  the 
ragged  and  serrated  crest  of  the  Argentiere  group  of 
the  Mont  Blanc  mountains.  A  largely  similar  struc- 
ture, although  lacking  the  needle-like  terminations,  is 
that  seen  in  the  "  saw-tooth "  crest  of  the  Sawback 
Mountains  of  South-western  Colorado,  and  in  the  so- 
called  Karren  of  the  limestone  Alps  of  Carniola,  Dal- 


THE  PHYSIOGNOMY  OF  THE  LAND-SURFACE.      193 

matia,  etc.  Cornice :  an  impending  part  or  true  cornice 
of  a  mountain.  More  generally  the  term  is  applied  to 
snow-fields  that  occupy  this  position,  and  in  which  there 
is  a  vertical  terminal  wall.  Couloir :  a  hollow  or  basin 
which  lines  up  to  an  arete  or  col,  and  occupies  a  posi- 
tion usually  below  the  full  summit  of  the  mountains. 
It  is  oftentimes  the  receiving-basin  for  the  formation  of 
glaciers  of  the  second  magnitude.  Massif:  the  great 
mass,  buttress,  or  nucleus  of  a  dominating  mountain. 
Clove :  a  recess  cut  by  water-action  into  the  wall  or 
heart  of  a  mountain  which  has  not  yet  developed  into 
a  full  valley.  In  some  of  its  accepted  forms  it  is 
synonymous  with  gorge,  ravine,  or  defile ;  but  perhaps 
with  clearer  definition  it  should  apply  only  to  such 
recesses  of  generous  development  as  terminate  abruptly 
in  the  mountain  itself,  and  which  lead  up  to  an  amphi- 
theatre or  circle  (cirque).  The  Kaaterskill  Clove,  in 
the  Catskill  Mountains,  and  the  upper  valley  of  Gavar- 
nie,  in  the  Pyrenees,  may  be  taken  as  the  type  of  this 
structure. 

In  their  inner  dress,  or  in  the  relations  which  they 
hold  to  the  rocks  which  build  them  up,  mountains  fol- 
low a  number  of  distinct  types.  Their  dependence 
upon  rock-foldings,  making  the  "anticlinal"  and  "syn- 
clinal "  mountains,  has  already  been  pointed  out  in 
Chapter  IV.;  and  it  now  only  remains  to  indicate  one 
or  two  types  of  construction  which  are  either  entirely 
independent  of  this  form  of  rock-movement,  or  are  in 
such  a  way  connected  with  them  as  to  make  the  associ- 
ation not  readily  discernible.  The  one  type  may  be 
designated  "faulted  mountain,"  where  the  elevation 
has  been  brought  about  through  an  uplift  along  a  line 


194  THE  EARTH  AND   ITS   STORY. 

of  fault ;  or  much  the  same  form  of  relief  (relative 
elevation)  will  result  from  a  downfall  along  the  line 
of  faulting.  Where  a  number  of  movements  have  fol- 
lowed on  distinct  but  parallelly  placed  lines  of  faulting, 
bringing  into  sharp  relief  successive  "  blocks  "  of  the 
earth's  crust,  we  have  presented  that  type  of  mountain 
construction  which  by  American  geologists  has  fre- 
quently been  designated  the  "Basin  Range  t}^pe," 
from  its  representation  in  the  Great  Basin. 

In  what  is  known  as  the  "monoclinal  mountain,"  we 
have  hardly  more  than  an  unimportant  modification  of 
the  type  that  has  just  been  described.  The  strain  that 
in  the  one  case  has  caused  absolute  disruption  of  the 
rock-mass,  with  either  upward  or  downward  movement, 
has  in  the  other  brought  about  merely  an  abrupt  bend- 
ing (or  "  kneeing ")  of  the  rocks ;  it  has  produced  a 
one-sided  fold,  or  monocline.  It  cannot  be  overlooked, 
however,  that  in  some  cases  the  monocline  is  merely 
a  greatly  elongated  anticline,  in  which  the  axis  of  the 
arch  has  been  removed  entirely  to  one  side. 

The  Physiognomy  of  Plateaus  and  Plateau  Moun- 
tains.—  Plateaus  in  some  regions  of  the  earth's  surface 
are  hardly  less  significant  physiographic  features  than 
are  the  mountain  chains.  Of  two  continents,  at  least, 
Africa  and  Australia,  they  are  the  dominant  features ; 
and  in  both  Asia  and  North  America  they  occupy  a  not 
insignificant  portion  of  the  entire  area.  In  its  more 
generally  received  definition,  a  plateau  is  any  large 
land-area,  not  distinctively  mountainous  in  its  surface 
aspect,  which  occupies  a  high  position  above  the  sea. 
As  such  it  presents  itself  to  us  in  a  variety  of  forms, 
not  all  of  which  have  the  same  geological  relation. 


THE  PHYSIOGNOMY  OF  THE  LAND-SURFACE.      195 

Two  broad  types  may  be  easily  recognized  :  "  mountain 
plateaus,"  or  such  as  have  a  distinct,  relation  to  the 
rearing  up  of  mountain  chains,  and  are  secondary  to 
them;  and  "continental  plateaus,"  of  much  greatei 
extent,  which  are  independent  of  primal  mountain  for- 
mation. Good  examples  of  the  first  class  are  found  in 
the  high  lands,  of  10,000  to  13,000  feet  elevation,  that 
are  held  up  between  the  enclosing  walls  of  the  Andes, 
in  somewhat  similar  regions  of  the  Rocky  Mountains, 
and  in  the  flattened-out  parts  of  the  Appalachian  Moun- 
tains, and  as  we  find  them  in  the  Pocono  Mountains  of 
North-eastern  Pennsylvania,  in  the  Catskill  Mountains 
of  New  York,  and  in  the  Cumberland  Plateau  moun- 
tains of  Tennessee.  In  the  examples  last  named,  the 
rocks  depart  but  little  from  the  horizontal  position,  and 
consequently  do  not  partake  of  that  folding  and  plica- 
tion which  might  be  said  to  be  the  essence  of  mountain- 
making.  Yet  the  regions,  through  varying  erosion, 
stand  up  prominently  like  every  other  mountain  tract, 
and  justly  lay  claim  to  being  considered  mountainous. 
Where  cut  out  of  plateau  masses  of  this  kind,  the 
elevations  may  properly  be  designated  "  plateau  moun- 
tains." (Plate  49,  Fig.  2.) 

As  types  of  the  continental  plateau,  may  be  taken 
the  great  inner  mass  of  South-central  and  East-central 
Africa,  extending  into  the  Soudan  and  Abyssinia,  and 
covering  (with  an  elevation  of  5,000  to  10,000  feet) 
hundreds  of  thousands  of  square  miles  of  hardly  dis- 
turbed rock-strata.  The  great  "  Tertiary  Plateau  "  of 
the  Western  United  States,  in  Colorado,  Utah,  and  Ari- 
zona, is  an  equally  good  type  of  this  structure.  On  its 
eastern  and  south-eastern  faces,  where  erosion  has  laid 


196  THE  EARTH  AND   ITS   STORY. 

bare  the  thousands  of  feet  of  nearly  horizontal  strata 
out  of  which  it  is  constructed,  and  equally  in  the 
numerous  canons  that  cut  into  it,  the  landscape  is  pre- 
eminently that  of  lofty  mountains ;  the  top  level,  on 
the  other  hand,  presents  the  typical  plateau  surface. 
It  seems  likely  that  the  uplift  of  this  plateau,  as  well  as 
of  that  of  Africa,  was  brought  about  through  a  bodily 
"  squeeze  "  of  its  rock-masses,  the  strata,  while  appear- 
ing horizontal,  being  in  fact  arched,  but  so  gently  and 
over  so  broad  an  expanse  as  to  virtually  escape  detec- 
tion. 

Another  type  of  plateau  is  furnished  by  the  interior 
of  Greenland,  and  by  seemingly  the  greater  portion  of 
the  central  mass  of  Mexico.  In  the  former  the  accumu- 
lation, through  ages,  of  falling  and  drifting  snow,  has 
blotted  out  the  normal  mountain  and  valley  features 
of  the  land,  and  raised  the  surface  to  a  general  level  of 
6,000  to  10,000  feet  elevation  —  the  most  uniform  pla- 
teau surface  that  is  known  upon  the  face  of  the  earth. 
Much  the  same  form  of  construction  is  to  be  found  in 
the  Mexican  plateau,  except  that  in  this  case  the  filling 
in  of  the  surface  irregularities,  or  the  making  of  the  pla- 
teau, has  been  brought  about  mainly  as  the  result  of  vol- 
canic discharges  —  the  outflow  of  lava  and  the  pouring 
over  it  of  an  almost  incredible  quantity  of  volcanic  ash. 

The  distinction  which  some  geographers  and  geolo- 
gists have  attempted  to  establish  between  plateau  and 
table-land  has  not  met  with  general  acceptance,  and  is 
not  founded  on  sufficiently  important  characters  to  war- 
rant recognition. 

The  Physiognomy  of  Valleys.  —  Valleys  properly  di- 
vide themselves  into  two  broad  groups,  —  valleys  of  the 


THE  PHYSIOGNOMY  OF  THE  LAND-SURFACE.      197 

mountains,  and  valleys  of  the  open  country.  The  latter 
are  more  generally  low-lying,  and  at  times  represent 
merely  the  old  sea-bottom  which  has  been  laid  and  kept 
dry  without  undergoing  serious  modification ;  of  this 
type  are  the  main  valley  of  the  Mississippi  and  most  of 
the  river  valleys  that  lie  on  the  coastal  plain  of  the 
United  States.  At  other  times  these  large  open  valleys 
are  the  made  land  of  river  sediment  —  a  reclamation  of 
territory  from  the  sea.  Such  are  the  great  "  plains  "  of 
much  of  low-lying  China,  the  "Netherlands"  of  North- 
western Europe,  the  valley  of  Lombardy  and  Yenetia, 
of  the  lower  Ganges,  etc.  As  a  type  of  the  great  open 
valley  occupying  a  high  position  may  be  cited  the 
western  half  of  the  Great  Plains  which  lie  between  the 
Mississippi  River  and  the  base  of  the  Rocky  Moun- 
tains —  the  valley  of  the  Platte,  etc.  Here  we  have  an 
extensive  area  of  fairly  ancient  sea-bottom,  elevated  to 
some  5,000  or  6,000  feet,  in  which  mountain  features 
have,  for  one  reason  or  another,  not  yet  been  developed. 
The  River  Platte  flows  on  the  surface,  instead  of  cut- 
ting its  way  down  in  the  manner  of  the  more  westerly 
canon  streams.  In  the  absence  of  those  sharply  defined 
mountain  features  which  define  the  canon  region,  — 
features  that  have  been  worked  out  mainly  as  the 
result  of  water  erosion,  —  we  prefer  to  call  this  surface 
"  plains  "  or  "  valleys,"  in  preference  to  plateau  (with 
its  valleys  lying  deep  down  in  the  canons)  ;  but  mani- 
festly the  distinction  of  terms  has  here  little  or  no 
significance. 

Mountain  valleys  are  such  as  originated  within  moun- 
tain areas,  and  were  determined  as  the  result  of  moun- 
tain-making. Their  relations  to  the  trend  of  the 


198  THE  EAETH  AND   ITS   STORY. 

mountains,  whether  longitudinal  or  transverse  valleys, 
and  their  significance  as  features  of  water  erosion,  have 
been  explained  in  Chapter  IV.  In  their  topographic 
aspects,  such  valleys  differ  from  one  another,  apart  from 
the  matter  of  size,  primarily  in  the  contours  of  their 
boundary  walls  and  in  the  width  and  inclination  of 
their  floors.  Broad  and  flat  valleys  belong  in  the 
main  to  the  lower  mountain  tracts,  where  the  work 
of  water  reconstruction,  the  deposit  of  sediment,  in 
great  measure  counterbalances  the  work  of  denudation, 
and  where  the  latter  represents  the  combined  work  of 
a  number  of  streams  united  into  a  single  one,  with 
broadly  distributed  labor,  instead  of  labor  in  a  re- 
stricted area.  In  such  valleys  the  abrupt  and  rugged 
features  of  the  landscape  have  been  largely  blotted  out, 
and  a  gently  flowing  outline  has  been  substituted.  The 
boundary  walls  slope  up  easily ;  and  between  them  is  a 
generous  expanse  of  flat  country  —  the  valley  itself. 
Geologists  have  been  in  the  habit  of  characterizing  val- 
leys of  this  description,  from  the  form  of  their  cross- 
section,  U-shaped  valleys,  in  distinction  to  the  abrupt 
passages  —  gorges,  ravines,  canons,  etc.  —  which  belong 
more  properly  to  the  upper  mountain  tracts,  where  the 
tumultuous  energy  of  single  streams  is  largely  empha- 
sized, and  where  the  contained  sediment  acts  in  itself 
as  an  eroding  agent  rather  than  as  an  agent  tending  to 
cover  up  the  work  of  destruction  by  its  own  deposition. 
This  type  is  known  as  the  Y-shaped  valley.  (Plates 
17,  18.) 

In  their  dominant  types  these  two  forms  of  valleys 
have  dually  different  significations  :  v  in  the  V-shaped 
valley,  nearly  all  the  energy  is  directed  to  down-cut- 


THE  PHYSIOGNOMY  OF  THE  LAND-SURFACE.      199 

ting;  at  least  the  cutting  in  this  direction  is  far  in 
excess  of  the  lateral  destruction  of  the  boundary  walls 
through  ordinary  atmospheric  agencies.  Hence,  the 
sharpness  of  the  cut  and  the  closeness  of  its  confining 
walls.  Especially  is  this  condition  emphasized  in  dry 
and  arid  regions,  such  as  the  western  canon  region, 
where  there  is  a  greatty  restricted  rainfall,  but  where 
powerful  streams  are  yet  present.  The  V-shaped  val- 
ley broadens  out  with  age,  and  ultimately  loses  its  dis- 
tinguishing characteristics.  It  is,  consequently,  spoken 
of  as  a  young  feature  in  the  landscape.  In  the 
U-shaped  valley,  the  lateral  destruction  keeps  pace 
with,  or  even  far  exceeds,  the  downward  cutting,  and 
thereby  obtains  its  open  and  flowing  outlines.  It  is 
oftentimes  merely  an  extension  in  time  of  the  V-shaped 
type,  and  hence  is  regarded  as  an  old  feature  in  the 
landscape ;  but  the  valleys  of  this  type  are  not  all 
necessarily  ancient. 

There  is  a  third  type  of  valley,  much  less  abundant 
than  either  of  these  two,  which  differs  from  them  in 
the  marked  flatness  of  its  floor,  its  open  extent,  and 
the  comparative  steepness  of  its  boundary  walls.  These 
are  the  valleys  which  are  or  recently  have  been  occu- 
pied by  glaciers,  and  have  been  doubtless  largely  fash- 
ioned by  them.  The  ice,  itself  eroding  in  part,  and  as 
a  cover  preventing  erosion  by  the  atmospheric  waters, 
has  thus  produced  a  contour  which  may  be  said  to  lie 
intermediate  between  the  two  types  that  have  been 
described. 

Physiognomy  of  the  Coast-Line.  —  The  most  obvious 
distinctive  features  which  coast-lines  present  are  em- 
bodied in  the  presence  or  absence  of  indentations,  and 


200  THE  EARTH  AND  ITS   STORY. 

in  the  presence  or  absence  of  prominent  elevations 
(bluffs,  cliffs,  promontories).  The  closed,  or  regular, 
coast,  is  well  developed  around  the  continent  of  Africa 
and  over  the  greater  extent  of  the  Pacific  side  of  Amer- 
ica ;  the  irregular,  or  indented,  coast,  finds  its  expres- 
sion in  the  Atlantic  border  of  Europe  and  in  the 
Pacific  contours  of  Asia.  Again,  the  bluff  coast  is  the 
characteristic  coast  of  Great  Britain,  while  the  flat 
coast  distinguishes  most  of  the  Atlantic  and  Gulf 
borders  of  the  United  States. 

The  contours  of  coast-lines  are  often  an  index  of 
the  special  phase  of  movement  that  characterizes  a 
given  continental  area.  Thus,  the  largely  indented 
coast,  and  the  coast  with  prominent  headlands  and  de- 
fining land-cliffs,  generally  determine  a  region  which  is 
now,  or  has  been  recently,  undergoing  subsidence,  or 
over  which  the  sea  is  rising;  the  closed  coast,  and  coast 
with  extensive  flat  reaches,  on  the  other  hand,  com- 
monly define  a  region  of  actual  or  recent  elevation,  or 
one  from  which  the  sea  has  only  latterly  receded.  This 
is  made  clear  when  we  recall  that  the  ocean,  as  an  agent 
in  the  equal  distribution  of  material  that  is  carried 
into  it,  tends  to  even  up  all  irregularities,  whether 
boundary  or  elevatory,  and  consequently  to  build  out 
under  its  protecting  waters  a  uniform  platform.  This, 
on  elevation  or  through  a  recession  of  the  waters, 
would  appear  as  a  great  expanse  of  flat  and  closed 
shore-strand,  much  like  the  Atlantic  littoral  of  the 
United  States.  On  the  other  hand,  a  subsidence  of 
the  land  or  transgression  of  the  sea  would  tend  to  a 
contrary  result,  to  an  emphasis,  through  the  destroying 
action  of  the  inflowing  waters,  of  such  irregular  fear 


THE  PHYSIOGNOMY  OF  THE  LAND-SURFACE.      201 

tures  as  the  land-surface  may  already  have.  It  is  in 
this  way  that  bays  are  extended  inward,  promontories 
lengthened  outward,  and  projecting  headlands  made 
steep  and  rugged  by  the  incising  action  of  the  beating 
surf  and  waves. 

The  relation  of  mountains  to  coast-lines  has  been 
referred  to  in  the  sections  devoted  to  the  physiognomy 
of  the  continents  and  to  that  of  mountains.  Many 
coast-lines,  especially  those  of  flat  reaches,  are  bordered 
by  more  or  less  parallel-trending  islets  and  islands,  — 
keys,  lagoon-barriers,  etc.,  —  as  we  find  along  almost 
the  entire  Atlantic  coast  of  the  United  States,  and 
again  off  the  north-west  coast  of  Germany  (Frisian 
Archipelago).  Such  structures  may  originate  as  sim- 
ple deposits  in  the  line  of  oceanic  currents,  being  in 
fact  built  up  by  them,  —  as  in  the  case  of  the  "  hooks  " 
and  barriers  which  bound  the  American  coast  for  the 
greater  distance  between  Long  Island  and  Florida,  —  or 
they  mayjbe  the  result  of  the  breaking  up  of  an  ancient 
flat  sea-front  by  an  oceanic  transgression  or  overflow. 
Of  this  nature  appears  to  be  the  line  of  islands  which 
lie  north  of  Holland  and  Germany,  and  constitute  the 
West  and  East  Frisian  Islands.  Thus,  the  barrier  fea- 
ture belongs  to  both  areas  of  stability  and  movement. 
The  presence  of  lines  of  rocky  islands  and  islets  off  a 
coast,  as  we  find  them,  for  example,  in  the  Lofotes  off 
Norway,  the  Shetlands  and  Orkneys  off  Scotland,  the 
Aleutian  Islands  off  Alaska,  and  the  South  Chilian  Ar- 
chipelago, is  almost  positive  indication  of  recent  conti- 
nental dismemberment,  —  either  as  the  result  of  direct 
continental  subsidence  beneath  the  sea,  or  of  the  rise  of 
the  water  over  the  land.  The  main  islands  of  Britain 


202  THE   EARTH  AND   ITS   STORY. 

are  themselves  merely  separated  parts  of  the  continent 
of  Europe  —  the  islands  of  Nova  Zembla,  the  broken- 
off  continuation  of  the  Ural  Mountains  in  the 
north. 

The  Physiognomy  of  Rock-Masses.  -  -  The  general 
aspects  of  rock-masses  have  been  referred  to  in  Chapter 
III. ;  and  it  remains  only  to  restate  some  of  their  funda- 
mental characteristics,  and  to  outline  other  essentials  of 
construction  and  position  which  have  not  been  referred 
to.  Fully  nine-tenths  of  all  the  rocks  that  are  known 
to  the  geologist,  barring  possibly  the  more  ancient 
rocks  of  the  metamorphic  series  (gneisses,  schists,  etc.), 
concerning  which  considerable  doubt  still  exists,  are 
transformed  ocean  sediments,  inorganic  and  organic 
(limestones).  As  such  they  were  accumulated  in  the 
trough  of  the  sea  in  either  horizontal  or  nearly  hori- 
zontal beds.  The  normal  position  of  rock-strata,  there- 
fore, is  one  not  departing  rigidly  from  the  horizontal; 
any  broad  departure  is  the  result  of  disturbance  follow- 
ing the  making  of  the  rock.  From  such  disturbance 
have  resulted  the  tilting,  folding,  overturning,  faulting, 
and  shearing  which  have  stood  the  rocks  vertically  (or 
on  their  edges),  pushed  them  over  one  another,  broken 
them  into  sections  and  pieces,  and  thrown  them  into 
parallel-trending  undulations  (mountain  folds).  From 
these  movements  have  resulted  those  types  of  structure 
which  we  have  already  learned  to  recognize  as  "anti- 
clines," "  synclines,"  and  "  monoclines,"  with  their 
attendant  "dips"  and  "strikes." 

Anticlines  (and  necessarily  also  synclines)  may  vary 
from  broadly  open  arcs  to  closely  compressed  zigzags, 
so  close,  in  fact,  that  the  opposite  faces  of  the  folds  are 


Plate  50. 


THE   PHYSICS   OF   MOUNTAIN-MAKING. 

The  results  in  "  folding"  obtained  by  squeezing  together,  from  the  ends,  a  series 
of  superimposed  layers  of  clay.  The  extent  of  pressure,  with  increase  of  fold- 
ing, increases  from  a  to  g.  A  laboratory  experiment  (after  B.  Willis). 


Plate  51. 


ROCK   FOLDS   AND  DISTURBANCES. 

The  surface  of  a  country,  under  erosion,  with  anticlinal  and  synclinal  structure; 
the  ridges  occupy  the  positions  of  the  harder  rock.  3  Analysis  of  a  fault. 
4.  5.  Analysis  of  anticlinal  and  synclinal  folds.  6.  An  angulated  fold  In  rock- 
strata,  with  incipient  fracture,  leading  to  a  fault.  7.  Fault,  with  vertical  dis- 
placement. (After  li.  Willis.) 


THE  PHYSIOGNOMY  OF  THE  LAND-SURFACE.      203 

made  virtually  parallel  with  one  another.  At  such 
times  it  is  frequently  exceedingly  difficult  to  determine 
the  presence  of  a  fold  at  all,  the  different  rock-strata 
seemingly  following  one  another  in  regular  and  direct 
sequence.  A  recourse  to  the  mineral  characteristics  of 
the  different  beds,  or  to  their  contained  fossils,  however, 
will  generally  determine  the  involution,  the  identical 
bed  recurring  in  two  or  more  places  in  the  same  sec- 
tion. In  the  making  of  an  anticlinal  fold  two  kinds 
of  strains  are  generally  imposed  upon  the  rock-masses : 
the  outer  beds,  by  reason  of  their  long  movement,  are 
pulled  apart,  while  the  inner  beds  are  in  a  measure 
compressed  through  shortening.  It  results  from  this, 
that  fractures  and  lines  of  weakness  are  developed  on 
the  anticlinal  crests,  which  are  rapidly  taken  advantage 
of  by  the  eroding  waters  in  their  general  course  of 
destruction.  Manifestly,  so  far  as  the  position  of  the 
rocks  is  concerned,  the  opposite  result  is  brought  about 
in  the  synclinal  fold. 

Anticlines  may  stand  singly  by  themselves,  or,  as  is 
more  often  the  case,  a  number  may  follow  one  another 
in  close  succession  and  parallelism.  The  ridge  of  the 
anticline,  the  summit-line  of  which  determines  the  di- 
rection of  trend,  or  strike,  of  the  rocks,  is  frequently 
designated  the  "anticlinal  limb;"  its  natural  crest, 
while  it  often  is  a  horizontal  line,  need  not  necessarily 
be  such,  but  may  decline  rapidly  to  the  horizon,  or  even 
alternately  rise  and  fall.  These  irregularities,  after 
denudation  has  materially  modified  the  original  relief 
of  the  land,  are  the  cause  of  much  complexity  in  the  sur- 
face contours  of  the  different  rock-strata ;  the  "  round- 
ing off"  of  strata,  surface  disappearance,  "spooning," 


204  THE  EARTH  AND  ITS   STORY. 

etc.,  are  conditions  with  which  the  geological  student 
will  sooner  or  later  familiarize  himself. 

Unconformity  in  /Succession.  —  Were  the  materials  of 
all  the  forming  rocks  of  any  one  region  permitted  to 
accumulate  and  develop  without  hindrance  or  disturl>- 
ance  of  any  kind,  the  rocks  that  would  be  formed  from 
them  ultimately  would  succeed  one  another  in  regu- 
lar conformable  lines  or  strata ;  the  inclination  or  dip 
of  one  stratum  would  be  the  dip  for  all.  Examples  of 
such  regular  succession  are  known  in  many  parts  of  the 
world  for  thousands  of  feet  of  thickness  of  rock.  But 
it  is  equally  true  that,  after  certain  series  of  rocks  had 
been  made,  they  were  subjected  to  more  or  less  violent 
movements,  which  had  the  effect  of  disturbing  their 
normal  positions ;  over  these,  at  a  subsequent  period, 
new  rock  material  was  again  laid  down,  and  in  a  nor- 
mally horizontal  position.  A  condition  of  unconformity 
has  here  been  established.  Unconformities  of  greater 
or  less  degree  occur  in  nearly  all  regions  where  two 
or  more  geological  formations  are  represented.  They 
offer  a  certain  time-measure  in  tracing  the  geological 
development  of  a  country,  inasmuch  as  they  are  the 
index  of  the  amount  of  work  (and  consequently  of  the 
time  required  to  do  this  work)  that  has  been  accom- 
plished since  the  rearing  up  of  the  earlier  rocks,  and 
the  disposition  of  the  newer  rocks  on  top  of  them. 
Frequently  the  older  rocks  show  barely  more  than  a 
trace  of  wear  along  the  divisional  line ;  at  other  times 
they  have  undergone  extensive  erosion,  or  have,  in  fact, 
been  even  eroded  almost  to  a  basal  level. 

G-eological  Breaks.  —  Under  this  term  geologists  un- 
derstand the  condition  when  a  hiatus  or  gap  intervenes 


THE  PHYSIOGNOMY  OF  THE  LAND-SURFACE.     205 

between  the  formations  of  any  given  region;  for  ex- 
ample, where  the  Carboniferous  formation  immediately 
follows  the  Silurian,  leaving  out  the  properly  inter- 
mediate Devonian  which  is  developed  elsewhere ;  or, 
where  possibly  the  Cretaceous  rests  directly  upon  the 
Carboniferous,  with  the  Permian,  Triassic,  and  Jurassic 
eliminated.  Occurrences  of  this  kind  are  indication 
that  vast  periods  of  time  had  elapsed  between  the 
deposition  of  the  older  and  the  new  rocks,  periods  suf- 
ficient in  which  to  have  accumulated,  in  more  favored 
regions,  the  deposits  that  normally  compose  the  geo- 
logical column.  The  fact  that  the  Devonian  deposits 
are  wanting  in  region  A,  and  the  Permian,  Triassic,  and 
Jurassic  in  region  B,  is  generally  taken  to  indicate  that, 
during  the  periods  when  those  deposits  were  forming 
elsewhere,  regions  A  and  B  were  removed  from  the 
ocean,  —  i.e.,  elevated  out  of  it,  —  and  could  not  receive 
marine  deposits  of  those  times ;  and  that  this  concep- 
tion is  in  a  general  way  a  correct  one  is  proved  by  the 
fact  that  areas  which  are  deficient  in  marine  deposits 
of  a  given  period  frequently  show  in  their  surfaces 
deposits  of  terrestrial  and  fresh-water  origin,  or  such 
as  would  be  formed  on  a  dry-land  area.  Gaps  of  this 
kind  may  be  measured  by  an  interval  of  but  a  few 
thousand  years  or  less,  or  they  may  extend  over  hun- 
dreds of  thousands  of  years,  time  sufficient  to  have 
completely  changed  the  character  of  the  world's  faunas. 
Hence,  we  frequently  find  in  strata  placed  in  immediate 
juxtaposition  the  most  diverse  types  of  plant  and  animal 
life  represented.  Such  diversity  is  always  an  indication 
of  a  vast  passage  of  time,  of  a  big  geological  break. 
Characters  Impressed  upon  Hock-Masses.  —  The  pres- 


206  THE  EARTH  AND  ITS  STORY. 

ence  in  the  solid  rock  of  many  of  the  distinctive  fea- 
tures that  ordinarily  belong  to  muds  and  sands,  such 
as  footprints,  raindrop  impressions,  ripples,  and  sun- 
cracks,  has  already  been  referred  to,  and  their  proper 
relation  to  the  acting  physical  forces  pointed  out.  There 
are  other  well-impressed  physical  characters  in  the  rocks, 
explainable  likewise  through  known  causes ;  but  they 
need  hardly  be  considered  here.  Reference  is  only 
necessary  to  what  are  known  as  "  current-bedding  " 
the  rapidly  alternating  and  shifting  stratification  which 
has  been  brought  about  by  irregular  currental  deposi- 
tion, as  when  near  the  mouth  of  a  stream  or  in  a 
delta  —  and  the  "  flow-and-plunge  "  structure,  a  wavy 
stratification  due  to  a  plunging  flow  of  a  stream  when 
depositing  its  sediment. 


COMMON  AND  MORE    USEFUL   METALS.          207 


CHAPTER   XVII. 

SOME  OF  THE  COMMON  AND  MORE  USEFUL  METALS 
AND  MINERALS. 

Gold  is  a  widely  distributed  mineral,  and  is  usually 
found  in  association  with  quartz  veins  of  mountainous 
and  volcanic  regions,  or  among  the  washings  (sand, 
gravel, '  river-mud)  that  have  been  derived  from  the 
destruction  of  the  parent  rock.  Its  more  general  form 
is  that  known  as  "native  gold,"  wliich  is  an  alloy  of 
about  ninety  per  cent  pure  gold  and  eight  or  ten  per 
cent  silver;  all  native  gold  has  silver  with  it,  and  in 
the  substance  known  as  electrum  the  quantity  of  the 
latter  amounts  to  about  twenty  per  cent.  Common 
or  native  gold  is  a  soft,  highly  ductile  and  malleable 
metal,  heavy  in  weight  (about  nineteen  times  the 
weight  of  water),  and  free  from  tarnish;  in  the  solid 
rock  it  occurs  as  strings,  flakes,  and  crystalloids,  fre- 
quently in  association  with  iron  pyrites,  and  occupying 
cavities  in  the  "  rotten  "  rock  which  have  been  left  by 
their  decomposition.  In  the  river-washes,  "  placer " 
deposits,  it  is  also  found  in  flakes,  grains,  and  scales, 
and  at  times  as  "  nuggets "  of  considerable  size  and 
weight.  Two  nuggets  from  the  Victoria  region  of  Aus- 
tralia weighed  respectively  2,280  and  2,166  ounces. 
The  most  productive  gold  regions  in  the  world  are 
those  of  the  Western  United  States  (California,  Colo- 


208  THE  EARTH  AND  ITS   STORY. 

rado,  Dakotas,  etc.),  Australia  (Victoria,  New  South 
Wales),  Russia  and  Siberia,  and  South  Africa;  in  the 
last-named  region  the  greater  part  of  the  output  is  from 
the  conglomerates  of  Witwatersrand. 

Much  of  the  silver  and  copper  that  are  mined  con- 
tain gold  mechanically  mixed  up  with  them,  a  circum- 
stance which  makes  specially  profitable  the  mining  of 
these  minerals ;  a  less  frequent  association  is  with  the 
sulphur  ore  of  lead  (galena).  Gold  hardens  through 
alloying  with  copper  and  silver;  the  former  tends  to 
give  the  compound  a  reddish-yellow  color,  and  the 
latter  a  distinct  greenish  shade.  In  the  gold  coin  of 
the  United  States  copper  is  present  in  about  a  tenth 
part.  The  metal  virtually  resists  all  ordinary  acids, 
but  is  soluble  in  a  mixture  of  nitric  and  hydrochloric 
acids  (aqua  regia).  A  compound  of  gold  and  tellurium 
makes  the  ricli  white  ore  known  as  Sylvanite. 

Silver  occurs  in  a  much  greater  variety  of  forms  than 
gold,  since  it  easily  unites  with  certain  mineralizers 
(such  as  sulphur,  bromine,  chlorine,  etc.),  to  form  a 
number  of  distinct  ores.  As  native  silver,  which  is 
not  common  except  as  an  alloy  of  gold,  it  occurs  in 
long  stringy  and  wiry  masses,  which  are  easily  folded 
and  twisted  upon  themselves ;  also  in  flakes,  scales, 
and  crystals.  A  specimen  of  native  silver  from  the 
mines  of  Kongsberg,  Norway,  and  now  in  the  royal  col- 
lection at  Copenhagen,  weighs  upwards  of  five  hundred 
pounds.  Like  gold,  silver  is  mainly  associated  with 
the  crystalline  and  igneous  rocks,  occurring  in  veins, 
lodes,  and  pockets.  It  is  a  soft,  highly  ductile  and 
malleable  metal,  with  a  specific  gravity,  as  compared 
with  water,  of  about  10.6  ;  its  normal  color  is  silver- 


COMMON  AND  MORE   USEFUL  METALS.         209 

white,  but  it  readily  tarnishes,  and  the  presence  of  only 
minute  quantities  of  sulphur  gas  in  the  atmosphere 
causes  it  to  enter  into  combination  and  turn  black. 
Native  silver  readily  dissolves  in  nitric  acid  (forming 
the  nitrate  of  silver),  from  which  it  can  be  easily  sepa- 
rated (precipitated)  by  the  addition  of  a  chlorine  com- 
pound, to  form  the  chloride  of  silver. 

The  greater  part  of  the  world's  silver  is  not  obtained 
from  the  native  metal,  but  from  one  of  its  several  ores, 
more  commonly  the  black  sulphur  ore  (sulphide),  Ar- 
gentite.  Two  forms  of  red  sulphur  silver  are  known  as 
Pyrargyrite  and  Proustite.  An  exceedingly  soft  com- 
pound of  silver  is  the  natural  chloride  or  horn-silver 
(Cerargyrite),  which  can  be  cut  almost  as  easily  with 
the  knife  as  resin.  Apart  from  these  sources  of  supply, 
an  important  repository  of  the  metal  is  found  in  the 
sulphur  ore  of  lead  (galena),  which  in  many  regions  is 
highly  argentiferous.  The  most  important  silver  pro- 
ducing countries  to-day  are  the  United  States  (Nevada, 
Montana,  Colorado,  etc.),  Mexico,  Bolivia,  Australia, 
Peru,  etc.  In  coin-silver  the  alloy  copper  makes  up 
about  the  one-tenth  part. 

Copper  occurs  native  in  strings,  grains,  plates,  and 
masses,  the  last  sometimes  of  gigantic  size ;  a  specimen 
is  recorded  with  a  weight  of  four  hundred  and  twenty 
tons.  It  is  a  soft  but  heavy  metal  (with  a  specific 
gravity  of  8.8),  and  can  generally  be  recognized  by  its 
distinctive  copper  color.  It  possesses  in  an  extreme 
degree  the  properties  of  malleability  and  ductility,  and 
is  an  excellent  conductor  of  both  heat  and  electricity. 
One  of  the  principal  uses  to  which  it  is  put  at  the  pres- 
ent day  is  the  making  of  copper  wire  foi*  the  conduct 


210  THE  EARTH  AND  ITS   STORY. 

of  the  electric  fluid,  largely  in  connection  with  the 
trolley  service.  A  large  proportion  of  the  world's 
copper  is  obtained  from  the  natural  metal,  with  which 
is  frequently  associated  a  workable  quantity  of  gold 
and  silver  ("auriferous"  and  "argentiferous"  copper); 
but  various  ores,  such  as  the  oxide  of  copper  {Cuprite), 
and  the  sulphides  of  copper  and  iron  (Bornite,  Chalco- 
pyrite),  contribute  largely  to  the  general  supply.  The 
leading  countries  furnishing  copper  are  the  United 
States  (Michigan,  Arizona,  Montana),  the  Iberian  Pe- 
ninsula, Chili,  and  Japan.  The  most  extensive  single 
deposit  of  the  native  metal  appears  to  be  that  of  Ke- 
weenaw  Point,  in  the  northern  peninsula  of  Michigan, 
where  is  located  the  famous  Calumet  and  Hecla  mine 
(depth  upwards  of  four  thousand  feet). 

Copper  is  not  restricted  to  any  one  class  of  rocks, 
but  its  largest  association  is  with  igneous  masses  and 
with  the  older  altered  series  (sandstones,  conglomerates, 
etc.).  Alloyed  with  zinc,  it  makes  brass,  and  with  tin 
(in  from  ten  to  twenty  per  cent),  bronze,  and  gun  and 
bell  metals;  statuary  bronze  is  usually  a  triple  com- 
pound of  copper,  tin,  and  zinc.  Of  the  more  familiar 
ores  of  copper  is  the  "  brassy  "  sulphide  of  copper  and 
iron  known  as  copper  pyrites  or  chalcopyrite,  which  has 
a  certain  resemblance  to  gold,  and  is  sometimes  mis- 
taken for  it;  hence  the  name,  "fool's  gold."  It  can, 
however,  readily  be  distinguished  from  gold  by  its  brit- 
tleness,  powdering  up  under  the  hammer  or  even  under 
the  well-pressed  knife-blade.  It  is  also  soluble  in  nitric 
acid,  whereas  gold  is  not;  and  in  addition  it  has  a  low 
specific  gravity  (about  4).  From  the  second  form  of 
fool's  gold,  or  iron  pyrites,  it  is  in  most  cases  easily  dis- 


COMMON  AND  MORE.  USEFUL  METALS.         211 

tinguished  by  its  deeper  coloring,  and  the  fact  that  it 
can  be  cut  with  a  knife,  whereas  iron  pyrites  cannot. 
A  highly  prized  ore  of  copper,  much  used  in  decorative 
purposes,  is  the  green  carbonate,  or  Malachite,  the  finest 
specimens  of  which  still  come  from  Siberia ;  the  blue 
carbonate,  which  frequently  passes  off  by  almost  insen- 
sible gradations  into  the  green  form,  is  the  beautiful 
mineral  known  as  Azurite. 

Zinc  as  a  pure  metal  is  not  known  to  occur  in  a  state 
of  nature.  That  which  is  used  in  the  arts  is  extracted 
from  one  or  more  of  the  zinc  ores,  most  largely  from  the 
zinc  sulphide  —  the  mineral  Sphalerite,  or  zinc-blende. 
This  mineral  is  usually  found  in  irregular  (or  partially 
crystallized)  masses,  of  a  translucent  grayish  or  yellow- 
brown  color,  with  a  distinct  resinous  ^lustre.  The  last 
characteristic  will  probably  serve  to  distinguish  it  more 
readily  than  any  other.  At  times  it  has  a  decided 
ugarnety"  appearance;  but  its  moderate  hardness,  3.5 
to  4,  easily  marks  it  off  from  garnet.  There  is  a  re- 
markable association  between  this  ore  and  the  common 
sulphide  of  lead  (galena),  the  two  being  so  generally 
found  together  in  the  same  deposits  that  they  are  fre- 
quently spoken  of  as  lead-zinc  ores.  What  the  nature 
of  this  association  is  has  not  yet  been  clearly  deter- 
mined. 

Among  the  more  important  uses  to  which  zinc  is  put 
is  the  manufacture  of  zinc-white  (the  oxide  of  the  metal 
zinc),  a  substitute  for  the  lead-white  of  paints.  Alloyed 
with  copper  it  makes  brass,  and  in  a  different  propor- 
tion the  so-called  "  white  metal."  The  coating  of  iron 
with  zinc  constitutes  the  process  of  galvanizing.  Other, 
but  much  less  common,  ores  which  yield  this  very  use- 


212  THE  EARTH  AND   ITS   STORY. 

ful  metal  are  the  red  oxide,  known  as  Zincite,  and  the 
silicate  {Calamine).  The  richest  yields  of  zinc  in  the 
United  States  are  in  Missouri,  New  Jersey,  and  Penn- 
sylvania. 

Tin,  if  it  occurs  at  all  in  a  native  metallic  state,  does 
so  very  rarely.  Its  most  common  ore  is  the  oxide,  when 
it  forms  the  mineral  species  Cassiterite,  or  tin-stone  — 
a  rich  brown,  hard  substance,  distinguished  in  its  crys- 
tallized form  by  a  beautiful  adamantine  lustre  and  high 
specific  gravity  (about  seven  times  that  of  water).  It 
occurs  disseminated  through  certain  granite  rocks ;  but 
elsewhere  it  is  found  in  rolled  grains  and  pebbles,  the 
so-called  "stream  tin,"  and  in  kidney-shaped  masses  of 
a  fibrous  structure  ("wood  tin").  In  the  arts,  tin  is 
extensively  used  as  a  coating  for  iron,  forming  in  union 
the  well-known  tin-plate.  With  copper,  in  various  pro- 
portions, it  constitutes  the  forms  of  bronze  known  as 
bronze  proper,  gun  metal,  bell  metal,  etc. ;  in  combina- 
tion with  lead  it  makes  pewter,  and  with  antimony, 
Britannia  metal.  Outside  of  Mexico,  the  American  tin 
deposits  have  little  importance ;  the  mines  of  Cornwall 
in  England,  and  of  Saxony  and  Bohemi ,,  have  been 
worked  for  centuries,  and  their  product  is  largely  sup- 
plemented by  the  output  from  Australia  and  the  East 
Indian  Archipelago. 

Lead,  which  is  one  of  the  most  familiar  and  useful  of 
metals,  and  in  its  ore  one  of  the  most  widely  dissemi- 
nated, is  so  rarely  found  pure  in  nature  that  it  might 
almost  be  said  not  to  exist.  That  which  is  commonly 
known  to  us  as  lead  ore  is  a  compound  with  sulphur, 
forming  the  mineral  species  G-alena.  It  occurs  in 
almost  every  kind  of  rock,  from  gneiss  to  volcanic  ex- 


COMMON   AND  MORE   USEFUL  METALS.          213 

trusions  and  limestones,  and  in  the  form  of  infiltrated 
and  penetrating  veins,  irregular  accumulations,  and  dis- 
tinct crystals.  It  is  almost  inseparably  associated  with 
the  sulphur  ore  of  zinc  (zinc-blende),  and  hence  the 
united  mass  is  not  infrequently  spoken  of  as  lead-zinc 
ore.  At  times  it  is  largely  silver-bearing  (argentif- 
erous) ;  and  this  fact  makes  the  mining  of  the  lead 
profitable,  when  by  itself  possibly  the  baser  metal  would 
have  yielded  little  in  returns. 

Galena  is  known  to  nearly  all  amateur  mineralogists 
in  the  beautiful  and  very  common  form  of  cubical  crys- 
tals, which,  when  not  tarnished,  may  have  an  almost 
brilliant,  although  still  leadeny,  lustre.  It  is  readily 
cut  with  a  knife,  being  one  of  the  softest  of  metals, 
and  leaves  a  dark  streak  on  paper.  Its  specific  gravity 
is  almost  as  high  as  that  of  metallic  iron,  about  7.5. 

The  various  uses  to  which  lead  is  put  need  hardly  to 
be  recounted.  As  an  alloy  with  tin  it  makes  pewter 
and  common  solder;  with  antimony,  the  substance  out 
of  which  printers'  type  is  manufactured  ("  type-metal"). 
In  the  making  of  leaden  shot  and  rifle-balls,  a  small 
quantity  of  arsenic  is  added,  which  makes  the  lead 
somewhat  harder,  and  in  addition  permits  it  to  assume 
a  spherical  form  when  dropped  through  the  air.  The 
carbonate  of  lead  furnishes  the  common  white  lead  of 
painters ;  it  is  also  the  principal  lead  ore  of  the  famous 
silver-lead  deposits  of  Leadville,  Colo.  The  largest  lead- 
producing  country  to-day  appears  to  be  Spain,  followed 
by  the  United  States,  Germany,  New  South  Wales,  and 
Mexico.  There  are  a  number  of  ores  of  lead  which 
are  highly  prized  by  collectors  for  their  beautiful  colors  ; 
among  such  are  the  grass-green  phosphate  (Pyromor- 


214  THE  EARTH  AND   ITS   STORY. 

phite),  the  orange-red  chromate  (^Crocoite),  and  deep 
red  vanadate  (Vanadinite). 

Antimony  as  a  native  metal  occurs  but  sparingly; 
it  is  a  bright  tin- white  mineral,  with  a  metallic  lustre, 
and  of  only  moderate  hardness.  The  antimony  of  the 
arts  is  obtained  from  the  sulphur  ore  of  the  metal,  anti- 
mony glance,  or  Stibnite,  of  which  Japan  furnishes  the 
largest  source  and  the  most  beautiful  specimens.  These 
are  elongated  prismatic  and  somewhat  spear-shaped 
(exceedingly  brittle)  crystals,  of  a  bluish-gray  color, 
and  with  brilliant  lustre ;  at  times  they  attain  a  length 
of  nearly  two  feet  or  more.  Antimony  is  mainly  use- 
ful in  the  arts  through  the  alloys  which  it  forms  with 
lead  and  tin,  imparting  to  both  greater  hardness  and 
durability.  Type-metal  is  a  compound  of  lead  and 
antimony;  Britannia  metal  is  an  alloy,  in  principal  part, 
of  tin  and  antimony. 

Arsenic,  like  antimony,  is  rarely  found  pure  in  nature  ; 
and  it,  too,  is  a  tin- white  mineral  with  metallic  lustre. 
Commercial  arsenic  is  obtained  principally  from  its  two 
sulphur  ores,  Realgar  and  Orpiment,  the  former  of  a 
beautiful  aurora-red  color,  and  the  latter  golden-yellow. 
Both  of  them,  although  by  no  means  abundant  minerals, 
occur  massive,  and  can  generally  be  recognized  by  their 
distinctive  coloring  (and  lustre)  and  exceeding  soft- 
ness ;  their  hardness  is  but  little  above  that  of  soap- 
stone.  The  compounds  of  arsenic  are  extensively  used 
in  the  manufacture  of  pigments,  for  preservatives,  in- 
secticide-poisons (Paris  green,  white  arsenic),  etc.  In 
the  making  of  leaden  rifle-balls  and  shot,  a  small 
quantity  of  arsenic  is  added  to  the  lead  to  give  it 
greater  hardness.  The  white  arsenic  (or  simply,  ar- 


COMMON  AND  MORE   USEFUL  METALS.         215 

senic)  of  druggists  is  the  oxide  of  the  metal,  and  is 
obtained  from  the  sulphur-arsenic  ore  of  iron  (inis- 
pickel)  by  roasting. 

Nickel.  —  This  metal  is  known  to  most  persons  in 
the  form  of  the  coin  "nickel,"  where  it  is  alloyed 
with  copper,  and  in  that  of  "nickel-plate,"  a  coating 
given  to  steel  which  resists  tarnishing.  German-silver 
is  a  compound  of  copper,  zinc,  and  nickel.  Most  of 
the  metal  of  commerce  is  obtained  from  nickel-bearing 
magnetic  and  copper  pyrites,  —  as,  for  example,  in 
the  important  mines  of  Lancaster  Gap,  Penn.,  —  and 
from  a  silicate  of  magnesia  and  nickel,  known  as  Grar- 
nierite.  The  latter  forms  the  chief  source  of  supply  in 
the  mining  districts  of  New  Caledonia.  An  exceed- 
ingly attractive  mineral,  conspicuous  at  times  by  the 
extreme  delicacy  of  its  needle-crystals,  is  the  sulphur 
ore  of  nickel,  Millerite  ;  it  also  occurs  in  fibrous  crusts. 
Nickel  is  almost  invariably  associated  as  an  alloy  in 
the  iron  of  meteorites.  A  new  industry  to  which 
nickel  has  been  applied  is  that  of  the  manufacture  of 
nickel-steel,  an  alloy  of  steel  with  about  four  per  cent 
of  nickel,  used  in  the  construction  of  armor-plating 
for  vessels. 

Iron,  through  its  vast  application  in  the  arts,  its  easy 
and  varied  manipulation,  and  the  facility  with  which 
it  can  be  obtained  in  quantity,  is  to  man  the  most 
important  of  metals.  There  is  hardly  a  region  of  any 
extent  where  it  does  not  occur  in  one  form  or  another, 
and  there  are  some  regions  which  yield  it  in  vast 
quantity.  Even  in  rock-masses,  where  its  existence  is 
not  made  directly  known  to  the  observer  by  the  obtru- 
sion of  the  mineral  itself,  in  the  form  of  crystal,  mass, 


216  THE  EARTH  AND  ITS   STORY. 

vein,  or  bed,  its  presence  is,  nevertheless,  often  attested 
sooner  or  later  by  the  formation  of  iron-rust.  The  coat- 
ings of  rust  on  marble  buildings  indicate  the  presence 
of  iron  within  the  substance  of  perhaps  an  apparently 
pure  marble.  So,  too,  the  accumulation  of  iron  scum 
on  meadow-bogs  is  an  indication  that  iron  has  been 
leached  out  from  some  of  the  neighboring  rocks,  and 
there  deposited  by  water.  Again,  the  various  colors 
of  rock-masses  are  in  themselves  largely  the  indica- 
tors of  the  presence  of  iron  in  those  rocks,  since,  in 
by  far  the  greater  number  of  cases,  the  varied  colors 
which  they  possess  are  merely  those  which  have  been 
given  to  them  through  iron  combinations,  usually  iron 
oxides. 

Iron  occurs  native  almost  exclusively  in  the  extra- 
mundane  meteorites,  where  it  is  usually  associated 
with  nickel,  and  in  certain  volcanic  rocks  (basalts)  of 
Greenland,  in  which  it  is  scattered  about  in  grains  and 
nodules.  The  great  iron-stones  of  Ovifak  and  Cape 
York,  Greenland,  which  were  at  one  time  thought  to 
be  meteorites,  and  show  many  of  their  characteristics, 
are  seemingly  of  telluric  or  earth  origin,  having  been 
forced  to  the  surface  through  eruptive  action.  The 
iron  of  commerce  is  obtained  exclusively  from  ores  of 
the  metal,  and  in  by  far  the  greater  quantity  from  the 
oxygen  ores,  the  oxides  of  iron  (.Hematite,  Limonite, 
and  Magnetite).  The  world's  annual  production  of  the 
metal  now  amounts  to  about  fifty  million  or  fifty-five 
million  tons,  of  which  the  United  States  (followed 
closely  by  Great  Britain)  alone  supplies  about  fifteen 
million  tons. 

The   most  important  ore  of  iron  is  the   red  oxide, 


COMMON  AND  MORE   USEFUL  METALS.          217 

known  as  Hematite,  which  occurs  in  a  variety  of  forms, 
from  massive  to  fibrous,  botryoidal,  earthy,  and  scaly, 
some  of  which  are  at  first  sight  difficult  to  recognize. 
It  has  a  brownish-black,  reddish,  or  black  color ;  but  its 
powder,  or  the  streak  that  is  put  upon  it  by  the  scratch 
of  a  knife,  is  invariably  red  (blood-red ;  hence  the  name, 
hematite  — blood-stone).  Its  hardness  is  such  as  barely 
to  permit  it,  except  where  crumbling,  to  be  incised 
by  a  knife-blade,  and  on  the  firmer  polished  forms  no 
cut  is  possible ;  its  specific  gravity  is  slightly  over  5. 
Some  of  the  blacker  forms  have  an  exceedingly  high 
polish,  reflecting  light  as  if  from  a  mirror  or  speculum 
(specular  iron) ;  at  other  times  the  lustrous  parts  are 
exceedingly  minute  and  scaly,  and  barely  distinguish- 
able from  the  mineral  mica  (micaceous  iron).  One  of 
the  earthy  forms  is  the  pigment  red-ochre.  The  im- 
portant iron  deposits  of  the  Lake  Superior  and  Ala- 
bama regions,  and  of  Iron  Mountain,  Missouri,  are  of 
hematite,  and  occur  in  regular  stratified  and  inter-strati- 
fied beds.  Some  of  it,  indeed,  in  the  Michigan  region 
has  replaced  whole  beds  of  limestone,  taking  the  place 
of  the  lime  by  slow  and  steady  substitution  following 
solution.  In  the  same  way,  some  of  the  Appalachian 
irons  have  replaced  the  original  materials  of  the  fossil- 
bearing  rocks,  and  have  replaced  the  fossils  them- 
selves ;  we  find  the  iron  marked  with  impressions  of 
shells,  corals,  encrinites,  etc.,  forming  a  true  "fossil- 
iferous  iron"  (also  known  as  Clinton  ore). 

Considerably  less  important  than  hematite, .  but  yet 
very  important  in  itself,  is  the  yellow  oxide  ore,  or 
Limonite.  It  has,  in  some  of  its  forms,  largely  the  ap- 
pearance of  the  preceding,  but  it  can  generally  be  dis- 


218  THE  EARTH  AND  ITS   STORY. 

tinguished  by  its  brown  color  and  yellow  streak  and 
powder.  It  is  largely  a  bog-deposit,  hence  "  bog-iron 
ore,"  and  is  frequently,  even  as  a  used  ore,  in  a  crumbly 
or  earthy  condition;  stalactitic  and  mammillary  forms 
are  not  uncommon.  Brown-ochre  pigment  is  manu- 
factured from  one  of  its  earths. 

A  third  oxide  ore  of  iron  is  Magnetite,  which,  as  the 
name  suggests,  has  the  distinguishing  quality  of  being 
magnetic,  i.e.,  of  being  attracted  by  the  magnet;  one 
variety,  known  as  lodestone,  is  a  true  magnet  in  itself. 
This  important  ore  of  iron  occurs  in  large,  one  might 
almost  say  mountain,  masses,  as  we  find  it  in  some 
parts  of  Pennsylvania  (Cornwall  Mines),  and  in  the 
Champlain  and  Adirondack  regions  of  the  State  of 
New  York.  A  frequent,  but  less  serviceable,  form  is 
that  of  octahedral  crystals  of  both  large  and  small 
size,  disseminated  through  schists  and  other  rocks ; 
these  are  often  found  protruding  from  the  surfaces  of 
broken-off  hand  specimens,  their  hard  points  easily 
distinguishing  them.  Particles  of  magnetite  are  also 
abundantly  disseminated  through  trap  and  other  rocks, 
from  which  they  are  liberated  through  weathering,  and 
are  then  scattered  about  in  the  waterways  of  streams. 
The  black  bands,  which  are  so  frequently  noticed  in 
the  courses  of  roadside  rills  and  rivulets,  are  largely  a 
construction  of  magnetite  particles.  An  iron  ore  much 
resembling  magnetite,  but  with  much  feebler  magnetic 
qualities,  and  having  in  its  composition  zinc  and  man- 
ganese in  addition  to  iron,  is  Franklinite. 

The  iron  known  as  "  spathic  iron  "  is  obtained  from 
the  carbonate  of  that  metal,  forming  the  mineral  species 
Siderite.  It  is  extensively  mined  in  some  regions,  but 


COMMON  AND  MORE   USEFUL   METALS.          219 

is  a  much  less  important  ore  than  those  that  have 
already  been  mentioned.  It  occurs  in  yellow-brown 
rhombohedral  crystals  of  only  moderate  density  (less 
than  4),  and  effervesces  when  treated  with  mildly 
heated  acids.  The  yellow  and  green  chrome  pigments 
are  obtained  from  Chromite,  or  chromic  iron. 

One  of  the  most  familiar  of  all  the  ores  of  iron,  but 
of  no  service  for  the  extraction  of  the  metal  itself,  is 
the  sulphur  ore,  or  Pyrites.  The  beautiful  and  highly 
lustrous  crystals  of  this  metal  are  known  to  almost 
every  one  who  has  worked  for  some  time  among  the 
rocks ;  for  they  are  of  very  broad  distribution,  and  are 
likely  to  occur  in  almost  any  kind  of  rock  —  slate, 
limestone,  quartz,  lava,  coal,  etc.  The  crystals  are 
cubes,  or  modifications  of  cubes,  of  a  brass-yellow  color, 
and  ordinarily  so  hard  as  to  completely  resist  the 
impression  of  a  knife.  This  fact  should  readily  dis- 
tinguish it  from  gold,  with  which  it  is  frequently  con- 
founded ("fool's  gold")  by  over-zealous  searchers  after 
the  noble  metal.  Its  greater  hardness  and  less  deep 
coloring  also  serve  to  distinguish  it  from  the  other 
form  of  "fool's  gold,"  copper  pyrites.  Iron  pyrites 
sometimes  contain  within  themselves  a  small  quantity 
of  gold  (sufficient  at  times  to  warrant  the  expense  of 
mining),  which  is  obtained  from  the  baser  metal  by 
smelting,  or  through  a  natural  process  of  rotting. 
Almost  the  only  service  to  which  pyrites  are  put  to- 
day in  the  arts  is  the  making  of  sulphur  and  sulphuric 
acid. 

Another  sulphur  ore  of  iron,  the  special  characteristic 
of  which  is  indicated  in  the  name  of  "  magnetic  pyrites," 
is  Pyrrhotite.  Its  reddish  or  bronze  color  readily  serves 


220  THE  EARTH  AND   ITS   STOET. 

to  distinguish  it  from  ordinary  pyrites.  The  frequent 
association  with  it  of  nickel  makes  it  one  of  the  valua- 
ble ores  of  that  metal. 

Manganese,  as  a  metal,  in  its  ore  associations  and  in 
general  chemical  behavior,  is  very  much  like  iron.  It 
does  not  occur  free  in  nature,  and  is  obtained  princi- 
pally from  its  two  oxygen  compounds,  Pyrolusite  and 
Manganite,  more  commonly  the  former.  It  is  largely 
associated  with  iron,  less  frequently  with  zinc  and 
silver;  and  in  one  form  or  another  occurs  in  nearly 
all  rocks,  from  sedimentary  to  eruptive,  and  virtually 
through  all  the  geological  periods.  It  is  readily  taken 
up  in  solution  by  water,  and  again  precipitated  by  it, 
following  closely  the  method  of  formation  of  bog-iron. 
To  nearly  every  one  it  is  familiar  in  the  fern-like  coat- 
ings or  crystal  forms  known  as  "dendrites,"  which  by 
the  uninitiated  are  frequently  mistaken  for  true  (fossil) 
fern  impressions ;  the  presence  of  the  metal  is  also  often 
de terminable  through  a  deep  brown  or  brown-black  stain. 
The  principal  application  of  manganese  in  the  arts  is 
the  alloying  of  it  with  iron  (Spiegeleisen)  to  make 
steel.  Pyrolusite  is  extensively  used  to  color  glass 
and  pottery,  and  produces  the  various  shades  of  violet, 
purple,  brown,  and  black. 

Mercury.  —  This  remarkable  and  exceedingly  useful 
metal  is  known  to  nearly  everybody  in  its  liquid  form 
of  quicksilver  —  the  substance  that  fills  the  bulb  and 
tube  of  mercurial  thermometers,  and  the  basin  and  tube 
of  mercurial  barometers.  It  is  the  only  mineral,  except 
ice,  which  remains  liquid  at  ordinary  temperatures ; 
but  while  the  former  melts  at  32°  F.,  mercury  remains 
liquid  until  the  very  low  temperature  of  —  40°  F.  is 


COMMON  AND   MORE    USEFUL   METALS.         221 

reached.  Native  mercury  is  a  rare  metal,  and  where 
occurring  it  is  generally  in  the  form  of  minute  globules 
scattered  through  the  rocks.  Nearly  all  the  world's 
mercury  is  obtained  from  the  sulphur  ore  of  that  metal, 
the  cochineal-red  mineral  known  as  Cinnabar.  This 
species  can  easily  be  recognized  in  the  combination  of 
its  three  most  distinctive  characters :  red  color  (with 
scarlet  streak  where  scratched),  great  weight,  and 
marked  softness,  being  easily  cut  with  a  knife.  Its 
weight,  which  exceeds  that  of  metallic  iron,  is  espe- 
cially noticeable,  but  it  is  far  below  the  weight  of  the 
pure  metal  (13.6).  Apart  from  its  service  in  the  con- 
struction of  thermometers  and  barometers,  mercury  has 
a  hardly  less  important  use  in  the  arts  through  its 
formation  of  amalgams,  compounds  of  mercury  with 
gold,  silver,  zinc,  tin,  etc.  The  "  silvering "  on  the 
backs  of  mirrors  is  ordinarily  an  amalgam  of  mercury 
and  tin.  The  "  amalgamation  process "  of  extracting 
gold  and  silver  from  rocks  in  which  they  are  contained 
consists  in  washing  or  agitating  the  powdered  rock 
with  mercury,  and  of  subsequently  reducing  the  gold 
or  silver  amalgams  that  have  thereby  been  formed 
through  the  simple  application  of  heat;  the  mercury 
is  driven  off,  and  the  gold  and  silver  are  left  behind. 

Mercury  is  variously  used  in  medicines,  but  its  active 
poisonous  properties  permit  it  to  be  dealt  out  only  in 
minute  doses ;  its  best  known  pharmaceutical  form  is 
calomel.  The  beautiful  pigment  vermilion  is  manufac- 
tured from  cinnabar.  Mercury  is  mined  in  quantity 
almost  exclusively  at  Almaden,  in  Spain ;  at  Idria,  in 
the  Austrian  crownland  Carniola  ;  and  at  New  Almaden 
and  New  Idria  in  California.  The  great  mine  of  Huan- 


222  THE  EARTH  AND  ITS   STORY. 

cavelica,  Peru,  which  between  1570  and  1790  yielded 
a  product  estimated  to  have  had  a  value  of  167,000,000, 
has  been  abandoned. 

Platinum  is  usually  classed  with  gold  among  the 
nobler  metab,  and  owes  its  great  value  chiefly  to  the 
fact  that  it  is  not  attacked  by  the  ordinary  acids,  and 
requires  an  enormous  temperature,  about  3,200°  F.,  to 
bring  it  to  a  state  of  fusion.  As  native  platinum  it 
is  not  pure,  but  contains  a  certain  (sometimes  large) 
admixture  of  iron  and  other  metals  (Palladium,  Rho- 
dium, etc.)  ;  as  such  it  is  usually  found  in  flakes  and 
nuggets  in  gold-bearing  gravels,  and  most  of  it  comes 
fro  in  the  Ural  Mountains  in  Russia.  Pure  platinum, 
as  obtained  through  artificial  process,  has  a  weight  con- 
siderably exceeding  gold  (21  to  22  times  that  of  water). 
From  the  manufacture  of  crucibles  and  the  making  of 
tooth-fillings  and  attachments,  the  special  use  of  plati- 
num has  developed  in  the  direction  of  electric  appliances 
(platinum  wires  of  incandescent  lamps,  etc.). 

Aluminium  or  Aluminum.  —  This  metal  has  of  recent 
years  obtained  deserved  recognition  as  one  of  special 
usefulness  in  the  arts,  and  primarily  through  the  double 
quality  that  it  possesses  of  extreme  malleability  and 
ductility,  and  its  light  weight.  The  pure  metal,  which 
is  not  found  native,  has  a  weight  less  than  that  of  ordi- 
nary limestone  or  calcite,  its  specific  gravity  being  rated 
at  2.5  ;  hence,  possessing  as  it  does  the  necessary  ten- 
sile strength,  it  is  made  exceedingly  valuable  in  the 
construction  of  articles  where  light  weight  is  considered 
a  desideratum.  Such  articles  are  found  in  military  and 
naval  equipments,  in  surveying  instruments,  racing  and 
other  boats  (even  to  steam-launches),  field-glasses,  etc. 


COMMON  AND  MORE   USEFUL  METALS.         223 

Aluminium  is  moreover  non-oxidizable,  and  readily 
lends  itself  as  an  alloy  to  iron,  copper  (aluminium 
bronze),  etc.  The  chief  source  of  the  commercial  alu- 
minium is  found  to-day  in  the  minerals  Cryolite  and 
Beauxite  ;  but  the  metal  finds  its  representation  in  the 
common  earths,  clays,  shales,  and  muds  by  which  we 
are  almost  everywhere  surrounded,  and  in  the  feldspar 
and  mica  constituents  of  the  granitic  and  schistose 
rocks.  These  are  in  the  main  silicates  of  alumina. 
Unfortunately,  the  association  of  the  metal  in  these 
compounds  is  such  as  to  debar  profitable  extraction 
with  the  methods  that  are  now  in  use.  The  advance 
in  the  aluminium  industry  may  be  inferred  from  the 
circumstance  that  forty  years  ago  the  cost  of  the  metal 
per  pound  was  from  $27  to  $90,  whereas  at  the  present 
day  it  is  considerably  less  than  a  dollar. 

The  oxide  of  aluminium  constitutes  the  mineral  co- 
rundum (the  grosser  forms  of  which  are  powdered  up  to 
make  emery),  which  in  certain  of  its  varieties  is  known 
under  the  names  of  sapphire,  ruby,  Oriental  amethyst, 
and  Oriental  topaz,  gem-stones  of  very  high  value  and 
beautiful  appearance.  Corundum  is,  next  to  diamond, 
the  hardest  of  minerals. 

Sulphur  is  in  many  ways  a  most  important  mineral, 
and  in  its  combination  with  various  metals  (silver,  lead, 
zinc,  antimony,  etc.),  forming  their  sulphides,  consti- 
tutes some  of  the  most  important  ores  of  those  metals. 
In  its  native  condition  it  is  a  beautiful  sulphur-yellow 
mineral  species,  occurring  either  massive  or  in  crystals, 
at  times  in  powder,  easily  cut  by  a  knife,  and  freely 
burning,  when  heated,  with  a  pale  blue  flame.  It  then 
disengages  the  suffocating  sulphur  gas  which  is  known 


224  THE  EARTH  AND  ITS   STORY. 

to  all  who  still  use  sulphur  matches.  Sulphur  is  largely 
associated  with  gypsum  deposits ;  but  in  most  part  it  is 
found  in  the  region  of  active  or  partially  quiescent  vol- 
canoes, sometimes  occupying  positions  with  the  ex- 
truded rocks  of  volcanoes,  or  forming  large  deposits  in 
their  craters  (as  we  find  it  in  Popocatepetl).  Its  use 
in  the  arts  is  largely  the  tipping  of  sulphur  matches, 
the  making  of  gunpowder  (with  charcoal  and  nitre), 
and  the  proper  preparation  of  the  rubber  for  gum-shoes. 
It  is  also  extensively  used  in  the  manufacture  of  sul- 
phuric acid,  but  of  late  years  much  of  the  sulphur  that 
is  used  for  this  purpose  is  obtained  from  the  yellow 
sulphur  ore  of  iron  (iron  pyrites). 

Graphite  or  Plumbago  is  familiar  to  every  one  in  the 
form  of  the  black  "  lead  "  of  lead-pencils.  It  is  a  soft 
iron-black  or  steel-gray  mineral,  which  occurs  in  mas- 
sive or  foliated  forms  in  the  older  crystalline  rocks, 
gneisses,  and  limestones;  it  can  be  easily  cut  with  a 
knife,  and  its  specific  gravity  is  only  a  little  above  2. 
One  of  its  distinctive  characteristics  is  to  streak  paper, 
making  marks  not  wholly  unlike  those  left  by  antimony- 
glance,  galena,  and  the  mineral  species  Molybdenite. 
Its  light  weight  and  distinctly  greasy  "feel"  readily 
serve  to  distinguish  the  mineral.  Its  soapy  character 
eminently  serves  to  make  it  useful  as  a  lubricator 
(when  pulverized),  and  its  resistance  to  great  heat 
permits  it  to  be  used  to  great  advantage  in  the  making 
(with  clay)  of  crucibles.  Most  of  the  commercial 
graphite  is  obtained  from  Siberia  and  other  parts  of 
Asia;  it  is  extensively  mined  in  Ticonderoga,  N.  Y., 
and  large  deposits  have  been  reported  from  various 
parts  of  Canada  and  Newfoundland. 


COMMON  AND  MORE   USEFUL  METALS.         225 

Rock  Salt  occurs  in  extensive  beds  in  many  parts  of 
the  world,  and  is  the  source  of  much  of  the  salt  supply 
of  the  world.  It  is  one  of  the  few  minerals  that  readily 
dissolve  in  ordinary  water  and  impart  to  it  a  distinct 
taste,  and  by  this  character  it  can  be  immediately  recog- 
nized. It  is  almost  as  soft  as  gypsum,  a  mineral  which 
it  frequently  resembles  and  with  which  it  is  largely 
associated,  and  like  it  is  in  part  an  oceanic  precipitate, 
and  in  part  a  lake  sediment,  accumulating  over  the 
floor  or  along  the  borders  of  desiccating  water-basins. 
As  the  chloride  of  sodium  (salt)  is  the  most  largely 
distributed  of  the  "salts"  held  in  solution  by  the 
oceanic  waters,  it  would  appear  only  natural  to  find 
many  of  the  ancient  oceanic  sediments  charged  with 
this  substance  ;  and  this  in  reality  is  the  case.  It  is  for 
this  reason  that  so  many  of  the  deep-seated  springs 
(artesian  waters,  etc.)  are  salty  when  they  come  to  the 
surface,  some  of  them  being  true  brines.  On  evapora- 
tion, these  brines  yield  nearly  pure  salt  —  a  condition 
that  applies  equally  to  the  waters  of  salt  lakes  and 
ponds  —  and  thereby  constitute  an  important  source  of 
supply  of  the  commercial  article.  Artificial  brines  are 
frequently  produced  by  admitting  water  to  the  seat  of 
the  deep-seated  rock-salt  deposits  and  then  pumping  to 
the  surface ;  the  water  of  exhaust,  being  evaporated, 
yields  a  resulting  salt.  Rock  salt  has  generally  a  vit- 
reous lustre,  and  may  be  white,  yellow,  red,  blue,  or 
even  black  in  color. 

Gypsum  can  be  recognized  very  readily  among  rocks 
by  its  moderate  hardness,  ranking  immediately  after 
soapstone,  and  being  easily  scratched  by  the  finger-nail. 
In  some  of  its  massive  forms  it  clearly  resembles  certain 


226  THE  EARTH  AND  ITS  STORY. 

limestones ;  but  the  quality  of  softness  immediately  dis- 
tinguishes it,  as  does  its  pearly  or  satiny  ("satin  spar") 
lustre.  The  variety  known  as  Selenite  (moonstone)  is 
to  a  high  degree  transparent.  A  common  form  that  is 
extensively  used  in  the  arts,  permitting  itself  to  be 
fashioned  by  almost  any  cutting  tool,  is  alabaster. 
Gypsum  is  in  composition  a  hydrous  sulphate  of  lime. 
On  heating,  the  water  is  rapidly  driven  off,  and  the 
mass  then  drops  to  powder.  This  is  the  well-known 
"plaster-of-paris,"  which,  when  again  united  in  proper 
proportions  with  water,  sets  hard,  and  forms  the  sub- 
stance which  we  recognize  in  plaster  casts  and  in  the 
hard  finish  of  walls.  The  quality  of  "  hardness  "  in 
spring-waters  is  largely  due  to  the  presence  of  gypsum 
in  solution.  Extensive  beds  of  this  mineral  are  found 
in  many  of  the  sedimentary  deposits,  and  in  some  cases 
appear  to  be  a  direct  oceanic  deposit;  at  other  times, 
it  is  a  lake  accumulation  or  precipitate,  forming  in 
those  bodies  of  water  where  an  excess  of  evaporation 
over  outflow  produces  general  saltness. 

Coal.  —  There  no  longer  exists  a  question  as  to  the 
vegetable  origin  of  coal.  In  many  varieties  of  coal  the 
woody  fibre  of  arboraceous  plants  can  clearly  be  made 
out;  in  others  the  mineralized  bark  is  well  preserved; 
and  in  still  others  the  microscope  plainly  demonstrates 
the  presence  of  millions  of  pollen-spores,  so  closely 
packed  together  as  virtually  to  make  up  the  mass  of  the 
coal  itself.  The  fact  that  the  rock  is  in  such  a  large 
proportion  pure  carbon  is  in  itself  sufficiently  sugges- 
tive of  a  vegetable  origin ;  but  as  to  the  precise  manner 
in  which  the  plant-tissues  were  turned  into  coal,  or  the 
approximate  conditions  which  governed  the  develop- 


COMMON  AND  MORE   USEFUL  METALS.        227 

ment  and  growth  of  these  plants,  considerable  doubt 
still  remains.  Some  coal  is  manifestly  merely  a  trans- 
formation of  the  black  muck  of  peat-bogs  —  a  long  con- 
tinued accumulation  of  growing  and  decomposing  fibres 
of  two  or  more  species  of  bog-mosses  (^Hypnum  and 
Sphagnum),  united  with  other  vegetable  substances,  and 
perhaps  a  certain  quantity  of  mud.  In  other  forms  of 
coal,  such  as  the  brown  coal  and  lignite,  woody  masses 
may  make  up  the  principal  part,  and  at  times  with  so 
little  alteration  in  their  substance  as  plainly  to  show 
in  the  mineral  their  full  cellular  or  fibrous  structure. 
For  the  greater  part  of  the  true  stone  coals  —  anthra- 
cites and  bituminous  coals  —  it  is  probably  safe  to 
assume  that  they  represent  a  vast  accumulation  of  vege- 
table debris,  which,  by  slow  stages  of  smouldering 
decomposition  and  accretion,  has  acquired  thickness 
and  mass  as  the  bottom  covering  of  swamps  and  river 
estuaries.  The  black  muck  accumulating  over  the 
floor  of  the  Great  Dismal  Swamp  of  Virginia  and 
North  Carolina,  in  the  cypress  tracts  of  Florida  and 
Georgia,  and  in  some  portions  of  the  estuaririe  tracts 
of  the  Mississippi  and  the  Amazons,  may  be  taken  as 
the  expression  of  coal  formation  at  the  present  day. 

The  most  extensive  coal-beds  of  the  world  —  those, 
for  example,  of  the  United  States  east  of  the  Rocky 
Mountains,  of  Great  Britain,  and  of  continental  Europe 
—  belong  to  the  Carboniferous  era ;  but  from  that  period 
of  time  to  the  present  coal  has  been  forming  almost 
continuously  in  one  region  or  another,  and  frequently 
not  passing  beyond  a  brown  coal  or  lignitic  stage.  In 
the  Rocky  Mountain  region  there  are  extensive  beds  of 
the  Cretaceous  and  Tertiary  ages,  and  in  California 


228  THE  EARTH  AND  ITS   STORY. 

good  coal  is  worked  in  the  Tertiary  deposits.  The 
older  coals  occur  in  alternating  beds  of  coal  and  shale 
("  underclay,"  "  fire-clay,"  "  roof-clay  "),  and  sand- 
stone, generally  neither  the  one  nor  the  other  of  great 
thickness ;  the  coal  itself  may  be  in  thin  inch-seams, 
developing  from  2  to  10  feet  or  more,  and  exceptionally 
attaining  20  or  30  feet  in  thickness.  There  may  be  as 
many  as  50  or  100  layers  of  dead  rock  and  coal  alter- 
nating with  one  or  another ;  and,  indeed,  in  a  few  places 
as  many  as  200  and  250  such  layers  have  been  indi- 
cated. The  alternating  beds  were  largely  the  soil  in 
which  the  coal-forming  plants  were  rooted,  but  the  fact 
that  they  frequently  contain  the  remains  of  marine 
organisms  (fossils)  within  themselves  makes  it  evident 
that  the  sea  frequently  encroached  within  the  coal-form- 
ing area.  In  other  words,  the  swamps  accumulating 
the  coal  were  in  direct  communication  with  the  sea,  and 
their  waters  must  necessarily  have  been  in  great  meas- 
ure salty.  The  main  coal  formation  of  the  United 
States,  extending  from  the  Appalachians  to  far  west  of 
the  Mississippi  River,  and  from  New  England  to  Ala- 
bama, gives  evidence  of  the  former  existence  of  a  vast 
swamp  or  morass  covering  hundreds  of  thousands  of 
square  miles. 

The  plants  of  these  older  coals,  although  at  times  of 
giant  proportions,  belonged  in  the  main  to  forms  which 
to-day  are  perhaps  most  nearly  represented  by  the  lowly 
club-mosses  and  horse-tails ;  Lepidodendron  and  Sigil- 
laria  rose  certainly  70  to  80  feet  in  height,  with  trunks 
4  or  5  feet  in  diameter,  and  Calamites  could  in  its  full 
development  hardly  have  been  less  than  40  feet.  None 
of  the  modern  type  of  trees,  except  possibly  some  coni- 


COMMON  AND  MORE    USEFUL   METALS.         229 

fers,  were  represented.  The  growth  was  a  surpassingly 
luxuriant  one,  —  tropical,  one  might  say,  in  its  density, 
—  but  it  gives  little  indication  as  to  the  temperature 
or  climate  under  which  it  nourished.  The  luxuriance 
of  the  forest  which  to-day  extends  to  the  glacial  lands 
of  Alaska  is  a  lesson  that  enforces  caution  in  dealing 
with  a  question  of  this  kind. 

Coal  in  its  different  forms  presents  us  with  a  large 
range  in  the  proportion  of  carbon  which  it  contains. 
In  the  best  anthracite  the  carbon  may  be  present  to  the 
extent  of  90  or  95  per  cent;  in  the  better  bituminous 
varieties  it  usually  makes  up  from  65  to  75  per  cent ;  in 
the  brown  coals  it  may  be  anywhere  from  30  to  50  per 
cent ;  and  in  peat  it  is  not  infrequently  reduced  to  one- 
half  of  this  amount,  or  even  considerably  less.  The  im- 
purities are  various  volatile  matters,  water,  and  greater 
or  less  quantities  of  mineral  ash.  Anthracite  appears 
to  be  in  most  cases  a  transformation  from  bituminous 
coal  through  heat  and  pressure,  conditions  brought 
about  by  rock-movements  or  through  volcanic  contacts. 
The  anthracites  of  the  world  —  those  of  the  Appalachian 
basin,  for  example  —  are  mainly  in  regions  of  great 
disturbance,  and  they  pass  off  gradually  into  the  less 
highly  carbonized  coals  that  occupy  the  contiguous 
areas  of  little  disturbance. 

It  is  assumed  that  there  may  be  in  this  country  about 
300,000  square  miles  of  coal-bearing  strata,  of  which 
the  Appalachian  district,  extending  from  Pennsylvania 
to  Alabama,  comprises  some  65,000  square  miles,  the 
central  area  (Indiana,  Illinois,  and  Kentucky)  some- 
what less  than  50,000  square  miles,  and  the  western 
area  (from  Iowa  to  the  .Rio  Grande)  about  100,000 


230  THE  EARTH  AND   ITS   STORY. 

square  miles.  Of  all  this  vast  area,  however,  hardly  a 
fifth  is  at  this  time  worked  or  coal-producing,  the  con- 
dition of  the  coal  being  such  as  not  to  permit  it  to  be 
mined  with  profit.  Nearly  all  the  anthracite  of  this 
country  is  obtained  from  the  anthracite  fields  of  Penn- 
sylvania, and  from  the  three  regions  which  are  gener- 
ally designated  the  Wyoming,  Lehigh,  and  Schuylkill. 
The  output  of  coal  in  the  United  States  amounted, 
in  the  year  1895,  to  194,000,000  (short)  tons,  of  which 
the  Appalachian  anthracite  fields  furnished  upwards  of 
58,000,000  tons,  and  the  State  of  Pennsylvania  alone 
(in  anthracite  only)  51,700,000  tons.  In  1895  the 
combined  anthracite  and  bituminous  output  of  Penn- 
sylvania amounted  to  110,000,000  tons.  Great  Britain 
(with  188,000,000  full  tons  in  1891)  is  still  the  largest 
coal-producer,  and  is  then  followed  by  the  United  States 
and  Germany  (94,000,000  tons). 

Petroleum  ;  Natural  Gas.  —  These  are  products,  seem- 
ingly, of  some  kind  of  natural  distillation  of  organic 
remains  —  remains  most  often,  probably,  exclusively 
vegetable,  at  other  times  animal  and  vegetable,  and 
less  frequently  only  animal.  At  least,  so  close  is  the 
resemblance  between  these  substances  and  certain  prod- 
ucts (oils  and  gases)  obtained  by  artificial  distillation 
from  organic  bodies,  that  such  reference  is  made  reason- 
able, and  it  does  no  violence  to  any  facts  that  are  known 
to  us.  The  source  of  both  petroleum  and  natural  gas 
is  found  mainly  in  the  deposits  of  Paleozoic  age,  from 
the  Lower  Silurian  to  the  Carboniferous ;  but  in  many 
regions  they  are  obtained  from  deposits  of  much  newer 
date.  Sandstones  and  conglomerates  are  most  highly 
charged ;  but  some  shales,  clays,  and  limestones  are  not 


COMMON  AND  MORE  USEFUL  METALS.         231 

entirely  deficient.  It  was  formerly  supposed  that  both 
petroleum  and  natural  gas  (which  is  largely  marsh  gas) 
stood  in  bonded  relationship  with  the  coal  deposits,  — 
from  which  it  was  assumed  they  were  obtained  through 
a  process  of  destructive  distillation;  but  the  fact  that 
both  are  so  largely  associated  with  rocks  of  much  older 
date  than  the  coal  makes  this  view  untenable,  or  at 
least  very  doubtful.  Both  petroleum  and  natural  gas 
show  rapid  exhaust,  a  proof  that  they  are  local  accumu- 
lations, and  do  not  replenish  —  at  least,  not  in  a  short 
period  —  as  do  the  natural  waters.  The  production  of 
petroleum  in  the  United  States  amounted  to,  in  1893, 
48,000,000  barrels,  of  which  New  York  and  Pennsyl- 
vania combined  furnished  20,000,000  barrels,  and  Ohio 
16,000,000. 

The  production  of  natural  gas  in  this  country  in 
1893  had  a  valuation  of  some  $14,000,000,  of  which 
Pennsylvania  furnished  about  one-half.  In  1888  this 
State  reached  a  maximum  output,  valued  at  $19,000,000, 
which  was  followed  by  a  rapid  decline,  due  mainly  to  an 
exhaust  from  the  worked  areas.  The  issuance  of  this 
gas  from  certain  wells  is  simply  prodigious,  the  produc- 
tion ranging  as  high  as  several  millions  of  cubic  feet 
per  day ;  but  a  rapid  outflow  is  almost  invariably  accom- 
panied by  a  steady,  sometimes  by  a  very  rapid,  decline. 

The  substance  known  as  bitumen,  or  asphaltum,  can 
properly  be  noticed  in  this  connection.  It,  too,  seems  to 
be  a  distillation  product  derived  from  organic  bodies, 
and  possibly  it  represents  a  stage  of  alteration  removed 
one  step  beyond  petroleum.  A  very  large,  and  perhaps 
the  main,  source  of  supply  of  this  substance  is  the  famous 
pitch  lake  of  the  island  of  Trinidad. 


232  THE  EARTH  AND  ITS   STORY. 


CHAPTER   XVIII. 

BUILDING-STONES,    SOILS,    AND    FERTILIZERS. 

Building-Stones.  —  Under  this  head  may  properly  be 
included  not  only  the  materials  that  are  directly  used 
in  construction,  but  such  as  lend  themselves  to  orna- 
mentation, to  design,  to  flagging,  and  to  other  related 
purposes.  These  are  the  granites  and  their  allies,  sand- 
stones, limestones  and  marbles,  shales,  and  slates,  all  of 
which,  in  their  geological  aspects,  have  been  discussed 
in  Chapter  II.  Numerous  considerations  determine 
the  possibility  of  using  stone  in  construction.  The 
matter  of  expense  in  quarrying,  the  facility  or  diffi- 
culty of  transportation,  proper  coloring,  consistency  of 
grain,  hardness,  resistance  to  crushing  strain  and  chemi- 
cal decomposition,  etc.,  —  all  have  to  be  considered ; 
and  it  is  rarely  that  all  the  desired  conditions  are  satis- 
fied in  any  one  construction.  For  general  purposes  the 
rocks  of  a  given  region,  even  if  of  inferior  or  unde- 
sired  quality,  are  used  in  the  neighborhood  by  prefer- 
ence over  superior  rocks  of  a  more  distant  locality,  as 
the  question  of  transportation  is  at  once  eliminated 
from  the  burden  of  delivery ;  and  in  truth  it  must  be 
said  that  there  is  hardly  a  region  of  granites,  of  sand- 
stone, or  of  limestone,  which  does  not  yield  a  fairly 
good  quality  of  building  or  monumental  stone.  Nat- 
urally, where  special  features  are  desired,  or  where 


BUILDING-STONES,   SOILS,   AND  FERTILIZERS.      233 

superior  strength  is  a  real  necessity,  as  in  the  construc- 
tion of  massive  buildings  and  in  piers  and  railroad 
abutments,  selection  becomes  imperative  ;  but  even  the 
most  careful  selection  is  at  times  only  sealed  misjudg- 
ment,  as  the  factor  of  chemical  decay  cannot  always  be 
determined  in  advance.  Oftentimes,  too,  the  manner  of 
placing  a  block  in  construction  will  have  much  to  do 
with  its  retaining  power;  regard  should  be  had  to  the 
protection  of  the  original  bedding-planes,  for  it  is  along 
these  that  the  destructive  water  is  apt  to  enter,  and, 
in  both  chemical  and  physical  ways,  begin  the  work  of 
disruption.  The  heat  of  the  sun,  combined  with  the 
cold  of  night,  forcing  alternate  expansion  and  contrac- 
tion of  the  rock,  is  also  a  disrupting  agent;  and  the 
amount  of  bad  work  done  by  it  will  in  great  measure 
depend  upon  the  extent  of  continuous  surface  that  is 
exposed  to  its  influence,  and  the  character  of  the  rock- 
face  that  it  acts  upon.  The  "peeling"  of  sandstones 
would  largely  be  prevented  were  proper  regard  had  to 
the  original  laying  of  the  blocks. 

Granites  of  a  homogeneous  and  moderately  fine  grain 
are  preferable  to  those  in  which  the  component  ele- 
ments are  largely  irregular  in  size,  and  make  up  a 
distinctly  coarse  texture.  The  Cape  Ann,  Quincy, 
Aberdeen,  and  Richmond  granites  have  long  been  con- 
sidered types  of  good  granites  ;  but  many  other  regions 
afford  equally  good  and  serviceable  stone.  Many  stones 
commercially  sold  as  granites  are,  however,  not  true 
granites ;  and  some  of  them  are  not  even  closely  related 
to  them.  Such  are  the  various  traps  and  diorites 
("  greenstones  ")  of  volcanic  origin  —  the  dike  mate- 
rial of  some  of  our  hills  and  mountains  —  which  are 


234  THE  EARTH  AND   ITS   STOET. 

extensively  used  in  road-paving.  Thus,  much  of  the 
"  Belgian  granite  blocks  "  of  our  city  streets  is  derived 
from  the  mass  of  the  Hudson  River  Palisades,  or  from 
other  igneous  extrusions.  Some  of  this  rock  is  fully 
as  resisting  as  granite,  and  is  therefore  allowed  to  meet 
(although  not  by  legal  recognition)  a  granite  specifica- 
tion. The  rock  known  as  Syenite,  which  is  wholly  or 
almost  entirely  deficient  in  quartz,  and  in  which  a 
black  hornblende  replaces  the  mica  of  true  granites, 
is  but  little  inferior  to  the  best  of  building-stones. 

Granite,  lacking  the  divisional  planes  of  stratifica- 
tion, would  ordinarily  present  insuperable  difficulties  to 
quarrying,  were  it  not  for  a  series  of  joint  planes,  or 
"  lines  of  jointing,"  which  usually  traverse  the  mass  in 
three  or  more  directions,  and  divide  it  up  into  quad- 
rangular or  dome-shaped  blocks  of  greater  or  less  di- 
mensions. These  lines  of  separation,  which  are  present 
in  greater  or  less  degree  also  in  sandstones,  limestones, 
etc.,  are  largely  due  to  contraction  on  cooling  from  a 
heated  condition,  and  in  other  part  to  dislocations 
which  the  rock  has  undergone  through  squeezing  and 
folding.  When  the  joints  follow  one  another  very 
closely,  the  granite  may  be  so  completely  cut  up  as 
to  render  it  unfit  for  quarrying  purposes  ;  at  other 
times,  hundreds  of  feet  may  intervene  between  the 
nearest  joints.  Another  series  of  traversing  lines,  which 
are  more  of  a  microscopic  character,  and  give  evidence 
of  weakness  by  a  tendency  of  the  rock  to  split  with 
smooth  fracture  planes,  are  known  as  "  rifts." 

Sandstones  are  ordinarily  good  building-stones,  but 
their  resistance  to  crushing  is  very  much  below  that  of 
granite ;  on  the  other  hand,  the  fact  that,  at  least  in 


BUILDING-STONES,   SOILS,   AND  FERTILIZERS.       235 

the  better  varieties,  the  rock  is  made  up  in  much  the 
greater  part  of  pure  quartz  grains  which  repel  the 
action  of  solvents,  makes  it  exceedingly  resisting  to 
chemical  disintegration.  This  is  especially  the  case 
when  the  binding  cement  is  also  siliceous ;  but  it  is 
much  less  so  when  this  is  lime,  which  readily  "  eats 
out,"  and  leaves  disagreeable  holes  and  cracks,  a  proper 
preparation  for  full  disintegration.  The  readiness  with 
which  certain  sandstones  absorb  and  retain  water,  which 
by  expansion  in  freezing  can  easily  disrupt  the  mass, 
emphasizes  caution  as  to  the  proper  selection  of  the 
required  variety  of  the  stone,  and  its  proper  placing 
in  construction.  The  unsightly  scars  brought  about 
by  "shaling"  or  "peeling"  of  the  surface  are  familiar 
disfigurements  of  even  stately  mansions.  In  the  East- 
ern United  States,  especially  in  large  cities  like  New 
York,  Brooklyn,  Boston,  and  Philadelphia,  the  sand- 
stone used  most  largely  in  house  construction  is  the 
well-known  "  brownstone  "  ("  new  red  sandstone  "  of 
geologists)  of  the  brownstone  fronts,  obtained  from  the 
Triassic  deposits  of  Pennsylvania,  New  Jersey,  and 
Connecticut.  The  central  States  of  the  Union,  more 
particularly  Ohio,  furnish  an  excellent  gray  or  cream 
variety  (Berea  stone,  etc.),  which  much  resembles  the 
famous  Fontainebleau  stone  of  France  (the  material  of 
construction  of  the  Paris  houses). 

Limestones  and  marbles,  when  of  good  quality,  also 
make  good  building-stones ;  and  while  it  is  true  that 
they  readily  lend  themselves  to  the  solvent  action  of 
the  carbonated  waters  of  the  atmosphere,  the  dissolu- 
tion is  so  slow  a  process,  and  takes  place  so  evenly 
when  the  substance  acted  upon  is  largely  pure,  that 


236  THE  EARTH  AND  ITS   STOEY. 

little  regard  is  had  for  this  condition.  Hence  it  is 
that  some  of  the  most  massive  buildings  of  the  world 
are  constructed  of  marble.  The  facility  with  which 
marble  is  quarried,  the  rock  being  marked  off  by  sepa- 
rating planes  of  bedding,  and  transversely  parted  by 
even  and  regular  lines  of  jointing,  and  the  readiness 
with  which  it  can  be  fashioned  by  the  cutting-tool,  are 
important  elements  tending  to  popularity  in  favor  of 
this  stone.  At  the  same  time  its  light  color,  assuming 
it  to  be  white,  rapidly  defaces  through  the  streaks  of 
iron-rust  which  sooner  or  later  appear  on  its  surface, 
the  evidence  of  iron  oxidation  taking  place  in  the 
interior.  Many  parts  of  the  United  States  furnish 
good  quality  limestones  and  marbles,  among  the  better 
known  of  which  are  the  Rutland  marbles  of  Vermont,  the 
Joliet  stone  of  Illinois,  and  the  Dayton  stone  of  Ohio. 
It  is  well  known  that  marble  is  used  for  various 
other  .purposes  besides  main  construction,  in  window 
and  door  facings,  interior  decorations,  etc.  Colored 
varieties  are  frequently  selected  for  interior  work ;  and 
as  marble  occurs  in  almost  all  shades  from  white, 
through  yellow,  blue,  and  red,  to  black,  no  difficulty  is 
met  in  securing  a  choice  of  design.  Some  of  the  fos- 
siliferous  varieties  make  handsome  decorative  slabs  for 
mantels,  table-tops,  etc.,  the  polished  surfaces  showing 
beautifully  the  fossil  forms  that  so  largely  make  up  the 
rock.  The  so-called  Tennessee  marble  is  a  limestone 
highly  charged  with  organic  fragments.  For  statuary 
purposes  the  Italian  (Carrara)  marble  is  still  preferred, 
owing  to  the  peculiar  tough-crystalline  structure  which 
distinguishes  it,  and  which  does  not  permit  it  to  crumble 
before  the  blow  of  the  chisel  and  mallet. 


BUILDING-STONES,   SOILS,   AND  FERTILIZERS.      237 

Flagging-Stones  are  most  commonly  large  slabs  of 
either  shale  or  shaly  sandstones,  and  less  often  lime- 
stones. In  selecting  these  materials  little  regard  is 
had  for  any  condition  beyond  extent  of  surface  and 
freedom  from  knotty  impurities;  the  latter,  if  present 
and  of  real  hardness,  weathering  or  wearing  out  into 
disagreeable  prominences.  The  ripples,  which  were 
originally  implanted  in  the  rock  at  the  time  of  its  mak- 
ing, frequently  show  up  well  after  the  paving  has  been 
used  for  some  time,  and  give  to  the  surface  of  the  stone 
a  wavy  or  undulating  appearance,  which  the  geological 
student  will  not  be  long  to  recognize.  Much  of  our 
flagging-stones  is  known  under  the  name  of  "blue- 
stone,"  and  is  obtained  from  the  almost  inexhaustible 
deposits  of  the  Silurian  and  Middle  Devonian  ages. 
Limestone  and  granite  flag-pavings  are  apt  to  become 
" gummy"  when  washed  over  with  water  and  mud, 
and  slippery  when  coated  with  snow,  and  are,  therefore, 
in  a  measure  objectionable.  Latterly,  the  introduction 
of  asphalt  and  "  artificial-stone  "  pavements  has  made 
considerable  headway,  and  is  likely  to  receive  increased 
favor  in  the  future. 

Roofing-Slates  and  Tile-Stones  occur  in  a  variety  of 
forms  ;  but  their  principal  differences  relate  only  to 
size,  thickness,  and  color  (red,  blue,  green,  black).  It 
is  true  that  the  composition  varies  considerably,  depend- 
ing largely  upon  the  presence  or  absence  of  a  certain 
quantity  of  lime ;  but  in  general  the  economics  of  the 
rock  depend  almost  entirely  upon  the  regularity  of  sur- 
face that  is  obtainable,  and  the  facility  with  which  it 
separates  into  thin  leaves.  Many  geologists  apply  the 
term  "  tile  "  or  "  tile-stone  "  to  the  shales  of  thin  bed 


238  THE  EARTH  AND  ITS   STORY. 

ding,  and  recognize  as  slates  only  such  aluminous  rocks 
as  break  off  or  "cleave  "  into  thin  plates  more  or  less 
transverse  to  the  planes  of  true  bedding.  This  form  of 
transverse  breakage  or  cleavage  seems  to  have  been 
brought  about  as  the  result  of  hard  tangential  pressure 
of  the  rock,  and  at  times  coincident  with  mountain- 
folding.  Hence  it  is  that  slates  of  this  character  are 
found  almost  exclusively  in  regions  of  great  disturb- 
ance, or  where  volcanic  extrusions  have  reacted  with 
violent  force  upon  the  rock- walls  which  formed  the 
boundaries  of  their  passage  toward  the  surface.  Lavas 
themselves  are  not  infrequently  cleaved  into  slates. 

Clays  and  Soils  are  in  many  cases  so  intimately 
bound  in  with  the  special  rock-formation  of  a  given 
region  that  it  takes  no  keen  eye  to  determine  that  they 
are  merely  a  derivative  product,  obtained  by  direct 
destruction  from  the  rock-masses  immediately  adjacent. 
The  red  dust  and  muds  overlying  decomposing  red 
shales  and  sandstones,  the  white  dust  and  sands  asso- 
ciated with  regions  of  light-colored  sandstones,  the 
sparkling  micaceous  particles  that  are  found  in  the 
soils  of  granitic  regions,  etc.,  clearly  point  out  this 
fact.  But  there  are  vast  areas  where  a  good  deal  of 
the  soil  is  a  stranger  to  the  place  where  it  is  found, 
having  been  brought  thither  from  possibly  distant 
regions.  Such  is  the  condition  of  the  regions  that  still 
lie  deeply  buried  beneath  the  "glacial  drift,"-— the 
vast  accumulation  of  bowlders,  gravel,  and  clay  which 
was  associated  with  the  steady  advance  over  the  country 
of  the  giant  glaciers  of  the  Great  Ice  Age  or  Glacial 
Period.  Geologists  speak  of  the  various  forms  of  these 
deposits  as  "bowlder  clays,"  "till,"  "drift,"  and  "brick 


BUILDING-STONES,   SOILS,   AND  FERTILIZERS.      239 

clays  "  (the  best  bricks  being  made  from  the  exceed- 
ingly fine  and  largely  homogeneous  clays  of  the  drift). 
In  some  regions,  on  the  other  hand,  as  in  parts  of 
Canada  and  Labrador,  there  is  little  or  no  soil,  what- 
ever existed  at  one  time  having  been  scoured  away 
from  the  rock  supporting  it  by  the  trespass  of  glacial 
ice. 

Soils  have  varying  characteristics,  and  adapt  them- 
selves in  different  ways  to  the  necessities  of  plant-life. 
Some  are  stiff,  holding  water  on  the  surface  (and  barely 
permitting  it  to  penetrate),  while  others  are  loose,  and 
allow  water  to  pass  as  if  through  a  sieve ;  a  medium 
condition  is  that  which  is  ordinarily  best  suited  to 
agricultural  purposes.  Excessive  ploughing  may  tend 
to  excessive  loosening,  a  condition  which  is  also  materi- 
ally favored  by  the  operations  of  the  earth-inhabiting 
animals,  such  as  the  ants,  earthworms,  and  even  moles. 
The  presence  of  clay-beds  tends  to  check  water-pene- 
tration, as  does  likewise  a  close  vegetable  growth  on 
the  surface.  Sandy  clay  soils  are  known  as  *'  loams," 
and  limy  ones  as  "marls ;"  but  under  the  name  of  marl, 
especially  in  the  Atlantic  border  region  of  the  United 
States,  is  frequently  included  a  series  of  earthy  de- 
posits which  in  fact  have  little  relationship  with  true 
marl,  and  of  which  an  essential  ingredient  is  the  green- 
ish silicate  of  iron  or  glauconite ;  hence  the  deposits 
are  also  known  as  "  greensands." 

The  fact  that  there  are  rock-beds  that  are  pervious, 
and  others  that  are  all  but  impervious,  to  water,  permits 
us  to  locate  the  position  of  the  water-bearing  series  — 
in  other  words,  to  determine  the  approximate  level  to 
which  the  water  may  have  penetrated  (through  sand- 


240  THE  EAETH  AND  ITS   STORY. 

stones,  limestones,  etc.),  and  where  it  is  now  held  up 
by  the  largely  impenetrable  clays.  This  is  an  impor- 
tant consideration  in  the  location  of  artesian  tappings ; 
as  it  determines  in  advance  the  amount  of  work  that 
will  be  required  to  obtain  the  needed  water-supply,  and 
the  probable  expenditure  that  such  work  would  entail. 
Fertilizers  ;  Lime,  Guano,  Phosphates.  —  The  pres- 
ence of  the  salts  of  lime,  potassium,  and  sodium  is  a 
condition  of  the  soil  that  meets  the  requirements  of 
plant-growth;  and  without  them,  either  in  part  or  in 
whole,  the  soil  becomes  fallow.  It  is  then  that  ferti- 
lizers are  needed  to  restore  the  life-giving  properties 
that  have  been  removed  from  it.  The  restoratives 
most  generally  in  use,  other  than  animal  and  vegetable 
manures,  are  lime  (burnt  from  limestones),  gypsum 
("land  plaster"),  and  various  forms  of  lime-phosphates, 
together  with  the  green  glauconitic  marls  to  which  ref- 
erence has  already  been  made.  The  lime-phosphate, 
constituting  the  mineral  species  Apatite,  which  is  meas- 
urably abundant  in  the  older  rocks  of  Canada,  has  a 
moderate  use  as  a  fertilizer ;  but  it  is  far  surpassed  by 
the  regular  rock  phosphates,  which,  in  nodular  and 
irregular  masses,  characterize  many  of  the  limestone 
deposits  of  the  Southern  United  States,  in  Florida,  Ala- 
bama, and  North  and  South  Carolina.  These  phos- 
phates, which  still  harbor  in  quantity,  in  the  shape  of 
teeth,  bones,  etc.,  the  remains  of  formerly  existing  ani- 
mals, have  unquestionably  been  formed  through  the 
agency  of  animal  decomposition  —  the  union  with  the 
lime  of  the  liberated  phosphoric  acid.  In  some  places 
the  animal  accumulations  make  true  "bone-beds,"  and 
as  such  are  admirably  adapted  to  soil-fertilization. 


BUILDING-STONES,   SOILS,   AND  FERTILIZERS.      241 

Most  of  the  more  important  phosphate  deposits  belong 
to  the  Tertiary  period  of  time.  In  certain  districts  the 
limestones  are  in  themselves  sufficiently  charged  with 
phosphatic  material  to  constitute  good  plant-food. 

The  excrement  of  various  forms  of  marine  birds, 
known  under  the  name  of  guano,  was  formerly  (and 
still  is  to-day,  to  some  extent)  an  important  source  of 
phosphatic  supply ;  the  most  extensive  beds  were  those 
of  the  Chincha  Islands,  off  the  coast  of  Peru. 


542  THE  EARTH  AND  ITS   STORY. 


CHAPTER    XIX. 

SOME    OF    THE    COMMONER    ROCK-FORMING    MINERALS, 
AND    MINERALS    OCCURRING    IN    ROCKS. 

Quartz,  rock-crystal,  or  silica  is  the  commonest  of  all 
minerals,  and  can  generally  be  recognized  by  its  glassy 
appearance  and  extreme  hardness,  ranking  as  7  in  the 
scale  of  hardness  which  is  generally  recognized  by  min- 
eralogists :  — 

Talc  or  Soapstone   ...  1  Feldspar 6 

Gypsum  (or  Rock-salt)     .  2  Quartz 7 

Calcite  or  Spar    ....  3  Topaz 8 

Fluor-Spar 4  Corundum     ....  9 

Apatite 5  Diamond 10 

It  is  the  substance  of  most  sea-shore  sands,  the  mate- 
rial of  sandstones,  and  one  of  the  three  essential  con- 
stituents of  typical  granite  and  gneiss.  In  chemical 
composition  it  is  a  union  of  the  elements  oxygen  and 
silicon.  It  occurs  in  undefined  or  amorphous  masses  or 
particles,  and  commonly  in  more  or  less  perfect  six- 
sided  (hexagonal)  prismatic  or  pyramidal  crystals.  A 
knife-blade  will  not  cut  it,  while  it  in  itself  readily 
scratches  glass ;  and  when  broken  across,  the  fracture- 
surfaces  are  almost  invariably  irregular  and  rounded 
(conchoidal). 

Quartz  occurs  in  a  great  variety  of  form  and  color; 
and  among  the  commoner  types,  as  determined  by  col- 


Plate  63. 


SOME  FORMS   OF   CRYSTALS. 

The  mineral  species  are  named  from  left  to  right  for  each  of  the  four  rows:  — 
1.  Quartz  (hexagonal  prism).    2.  Zircon.    3.  Fluorite  (octahedron).    4.  Garnet  (trapezohedron). 
5.  Quartz  (modified  hexagonal  prism).    Q,  Rock-Salt  (cube). 
7.  Gypsum.     8.  Quart/.     9.  Calcite  (rhombohedron). 
IO.  Emerald  (hexagonal  prism),     il    Gypsum.     12.  Topaz.     13.  Staurolite  (intercrossing-twin). 


COMMONER   ROCK-FORMING  MINERALS.        243 

oration,  we  recognize  black-  or  smoky-quartz,  rose- 
quartz,  yellow-  or  citron-quartz,  white-  or  milk-quartz, 
and  the  transparent  crystalline  rock-crystal ;  the  last 
named  is  the  Rhine-stone,  "Cape  May  Diamond,"  "Lake 
George  Diamond,"  etc.,  of  commerce.  More  highly 
prized  or  less  common  varieties  are :  Amethyst,  a  fine 
purple  kind ;  Camelian,  a  red  variety  with  a  waxy 
lustre ;  Opal,  an  opalescent  form,  showing  frequently 
a  beautiful  play  of  colors ;  Chalcedony,  a  more  or  less 
translucent  or  transparent  variety  of  a  dull  color  and 
with  a  certain  waxy  lustre ;  Agate,  a  variegated  Chalce- 
dony, with  the  colors  arranged  in  distinct  bands  ;  Onyx, 
very  much  like  Agate,  with  usually  white  and  black  (or 
brown)  bands  arranged  in  even  planes;  Sardonyx,  like 
Onyx,  but  with  red  bands  in  association  with  the  white 
or  black;  Chrysoprase,  an  apple-green  Chalcedony; 
Heliotrope  or  "  Blood-stone,"  a  dark  green  variety  with 
scattered  spots  of  red ;  Jasper,  an  opaque  variety  of  a 
green,  brown,  or  red  color,  frequently  banded  in  color ; 
Flint,  an  opaque,  dull  quartz,  usually  of  a  dark  or 
nearly  black  color;  Chert  or  Horn-stone,  an  impure, 
brittle  flint,  more  commonly  of  a  grayish  or  brownish 
color;  Lydian-stone  or  touchstone,  a  velvet-black,  flinty 
form,  frequently  used  for  testing  the  purity  of  metals  ; 
and  Cat's-Eye  (this  name  is,  however,  applied  to  other 
minerals) . 

Quartz  or  silica  is,  again,  the  substance  of  silicified 
trees,  or,  in  the  form  of  opal,  of  wood-opal,  which  is 
much  the  same  thing. 

Calcite,  or  as  it  is  frequently,  but  not  very  correctly, 
termed  "  spar,"  is,  after  quartz,  the  most  common  of 
mineral  species.  It  likewise  occurs  in  massive  and  in 


244  THE  EARTH  AND   ITS   STORY. 

crystalline  forms ;  as  the  first,  it  is  the  substance  of  shell, 
limestone,  marble,  and  chalk,  and  of  the  cave-deposits 
known  as  stalagmites,  stalactites,  and  stalactitic  crusts 
(Mexican  uonyx,"  etc.).  Its  various  crystalline  forms 
(in  rhombohedrons,  scalenohedrons)  are  ordinary  calc- 
spar,  nail-head-spar,  dog-tooth-spar,  and  Iceland-spar  (a 
beautiful  transparent  variety). 

Calcite  occurs  in  a  great  variety  of  color,  ranging 
from  white  through  yellow,  green,  blue,  pink,  and 
black.  In  its  truly  crystalline  forms  it  has  the  glassy 
appearance  of  quartz  ;  but  it  can 'be  readily  distinguished 
by  the  facility  with  which  it  is  cut  by  a  knife-blade, 
and  its  characteristic  of  undergoing  rapid  solution  in 
almost  any  acid,  with  a,  free  liberation  of  bubbles  of  car- 
bonic acid  gas.  This  property  of  effervescing  belongs  to 
nearly  all  carbonates,  the  carbonic  acid  of  their  com- 
position being  driven  off  or  liberated  by  the  stronger 
acid.  Calcite  is  chemically  a  compound  of  carbonic 
acid  and  lime  (a  carbonate  of  lime). 

A  mineral  Aragonite,  closely  related  to  calcite,  and 
having  its  chemical  composition,  should  be  mentioned 
here ;  also  a  second,  Dolomite  or  pearl-spar,  which  is  a 
double  carbonate  of  lime  and  magnesia.  Many  of  the 
giant  limestone  mountains  of  the  world,  such  as  the 
famous  Dolomites  of  the  Tyrol,  are  made  up  in  greater 
part  of  this  mineral,  as  are  likewise  some  of  the  finest 
statuary  marbles. 

Feldspar  is,  after  quartz  and  calcite,  the  most  abun- 
dant and  important  of  rock-forming  minerals.  It  is  one 
of  the  essential  constituents  of  granite  and  the  granitic 
rocks,  also  of -the  gneisses,  and  is  the  substance  which 
generally  imparts  the  distinctive  coloring  to  those 


COMMONER   ROCK-FORMING  MINERALS.        245 

rocks  ;  thus,  red  or  flesh-colored  granite  is  largely  con- 
structed of  pink  or  reddish  feldspar,  green  granite  of 
green  or  greenish  feldspar,  etc.  It  can  easily  be  distin- 
guished in  most  cases  from  the  quartz  with  which  it  is 
associated  in  these  rocks  by  its  color  —  the  quartz  being 
almost  invariably  gray  —  pearly  (not  glassy)  lustre,  and 
by  its  breakage-surfaces,  which  are  generally  flat,  and 
not  irregularly  curved  or  granular.  It  is  also  some- 
what less  hard  than  quartz,  and  can  at  times  be  in- 
dented with  a  knife. 

In  composition  feldspar  does  not  differ  very  greatly 
from  ordinary  earth  or  clay ;  indeed,  it  is  from  the  de- 
composition of  feldspars  that  much  of  the  material  of 
soil  is  obtained.  Porcelain-earth,  or  Kaolin,  is  also  a 
product  of  its  decomposition.  It  is  a  compound  of 
silica  and  alumina  (silicate  of  alumina),  with  potash, 
soda,  or  lime  added  to  these  substances.  The  most 
common  form  of  feldspar,  and  that  which  is  found  most 
generally  in  granitic  rocks,  is  the  potash-feldspar,  or 
Orthodase  ;  its  hardness  alone  will  suffice  to  distinguish 
it  from  calcite,  which  it  sometimes  closely  resembles. 
Of  its  varieties  are  the  clear  and  glassy  forms  known 
as  Adularia  and  Sanidine ;  also  the  somewhat  opal- 
escent moonstone.  The  beautiful  blue-green  feldspar 
found  near  Pike's  Peak,  Colo.,  and  in  Liberia,  known 
as  Amazon-stone,  has  the  composition  of  orthoclase. 

A  not  uncommon  feldspar  is  that  containing  soda, 
and  known  as  Albite,  from  its  common  coloring.  Of 
the  feldspars  containing  lime  and  soda  should  be  men- 
tioned Oligodase  and  Labradorite,  the  latter  often 
showing  a  beautiful  play  of  color,  with  peacock-blue  as 
its  base. 


246  THE  EARTH  AND  ITS   STOBY. 

Apart  from  their  ordinary  occurrence  as  essential 
components  of  granitic  rocks,  feldspars  often  unite  with 
quartz  to  make  veins  and  dikes  penetrating  the  granitic 
rocks,  sometimes  in  exceedingly  coarse  form,  with  the 
feldspar  developing  into  massive  crystals.  These  crys- 
tals not  infrequently  measure  a  foot,  or  even  consider- 
ably more,  across. 

Mica  is  an  important  rock  constituent,  as  it  is  one  of 
the  parts  of  typical  granites  and  gneisses,  and  the  most 
distinctive  part  of  the  vast  system  of  rocks  which  Lear 
the  name  of  mica-schists.  It  is  distinguished  from  all 
minerals  by  its  very  perfect  cleavage,  which  permits  it 
to  be  split  up  into  exceedingly  thin  sheets  or  leaves. 
These  are  used  for  various  purposes,  one  of  the  most 
common  being  the  "  glazing  "  of  stove-doors  (as  such 
incorrectly  called  "isinglass");  in  some  regions  the 
larger  plates  are  also  used  for  windows.  In  the  com- 
moner forms  of  micaceous  rocks,  it  occurs  generally  in 
small  scales  or  in  more  or  less  perfect  crystalline  forms 
of  from  a  half-inch  to  an  inch  in  diameter;  but  in 
certain  regions,  as  where  the  mineral  is  commercially 
mined,  plates  are  not  infrequently  removed  which  meas- 
ure two,  or  even  three,  feet. 

The  micas  are  essentially  silicates  of  alumina,  with 
potash,  magnesia,  and  iron,  and  more  rarely  soda,  added. 
The  commonest  variety,  and  that  which  is  used  com- 
mercially, is  the  potash-mica,  or  Muscovite,  ordinarily 
called  white  mica.  It  is  the  silver-white  variety,  at 
times  completely  transparent,  even  in  thicknesses  of 
many  layers :  but,  again,  it  shows  a  tendency  to  smoky 
color ;  and  when  this  is  well  emphasized,  especially  in 
many  thicknesses,  it  passes  off  in  the  direction  of  the 


COMMONER   ROCK-FORMING   MINERALS.         247 

next  species,  Biotite,  the  so-called  black  (also  deep 
green)  mica,  a  magnesia-iron  form.  Modifications  of 
this  species  are  the  brown  or  coppery-red  Phlogopite, 
and  the  singular  star-mica,  the  latter  showing  a  clear 
six-rayed  star  when  a  candle-flame  is  viewed  through  it. 
An  interesting  lilac  or  pink  mica  is  Lepidolite,  in  which 
lithia  is  the  accessory  mineral;  Margarite,  or  pearl- 
mica,  as  the  second  name  clearly  implies,  has  a  distinct 
pearly  lustre  on  its  cleavage  surface. 

Hornblende,  or  Amphibole,  which  is  a  common  acces- 
sory mineral  in  granites  and  gneisses,  forming  hornblen- 
dic  granites,  etc.,  can  generally  be  recognized  by  its 
hardness,  lustre,  and  dark,  black  or  almost  black,  color. 
In  small  scales  or  flakes,  it  much  resembles  black  mica, 
and  is  often  mistaken  for  it  by  the  young  mineralogist ; 
but  it  does  not  flake  off  like  that  mineral,  nor  can  it  be 
cut  easily  (if  at  all)  by  a  knife.  It  is  essentially  a  com- 
pound of  silica,  magnesia,  and  alumina  (a  silicate  of 
magnesia,  with  alumina).  Sometimes  it  is  so  abundant 
as  to  build  up  a  solid  rock  by  itself,  hornblende  rock ; 
or,  where  alternated  off  with  particles  of  another  min- 
eral species,  as  quartz,  hornblende  schist.  It  has  a 
hardness  of  5-6,  and  a  vitreous  or  pearly  lustre. 

Nearly  related  to  hornblende  are  Actinolite,  a  beauti- 
ful green  or  greenish  mineral,  often  occurring  in  fibrous 
or  radiated  masses ;  Asbestus,  a  very  fibrous  white  or 
gray  mineral  (silicate  of  magnesia  and  lime),  which  is 
at  times  woven  into  an  incombustible  paper  or  cloth ; 
and  Mountain-leather,  an  asbestus-like  substance  occur- 
ring in  tough  sheets  of  interlaced  fibres. 

Pyroxene,  likewise  a  silicate  of  magnesia,  with  lime, 
alumina,  or  iron  added,  has  much  the  habit  of  horn- 


248  THE  EARTH  AND  ITS   STORY. 

blende  ;  and  like  it,  it  has  a  variety  of  associations.  Its 
hardness  is  rated  at  5.5  to  6  ;  it  also  has  a  vitreous 
lustre,  and  in  color  varies  from  gray  to  green  and  black. 
One  of  the  commonest  and  most  important  varieties 
of  this  mineral  is  the  black  or  greenish-black  Augite, 
which  enters  so  largely  into  the  composition  of  some  of 
the  volcanic  rocks,  as  trap  (basalt,  diorite,  greenstone). 
Minerals  related  to  pyroxene,  or  forming  varieties  of  it, 
are  Diallage,  a  foliated  mineral  of  a  green  color;  En- 
statite,  which  by  decomposition  seems  to  yield  talc  or 
soapstone ;  Hyperstliene,  a  silicate  of  magnesia  with  con- 
siderable iron,  and  at  times  with  an  almost  metallic 
lustre  ;  and  Bronzite,  a  ferrous  variety  of  enstatite. 

Garnet  is  one  of  the  commonest  and  most  abundant 
of  the  accessory  minerals  contained  in  rock-masses.  Its 
usual  association  is  with  granites,  gneisses,  and  mica- 
schists,  especially  the  last  two,  in  which  it  occurs  in 
well-defined  crystals  of  (commonly)  twelve  or  twenty- 
four  sides  (dodecahedron,  trapezohedron),  and  of  sizes 
varying  from  a  pin's  head  to  three-quarters  of  an  inch 
or  more  ;  some  of  the  Colorado  garnet  crystals  measure 
three  inches  across,  and  weigh  from  three  to  five 
pounds.  The  gneisses  and  mica-schists  are  sometimes 
so  full  of  this  mineral  as  to  appear  completely  peppered 
by  it,  and  the  latter  is  virtually  converted  into  a  garnet- 
schist.  Again,  garnet  itself  sometimes  occurs  massive, 
so  as  to  make  a  distinct  garnet-rock.  In  composition 
it  is  essentially  a  silicate  of  alumina,  with  additions  of 
lime,  magnesia,  iron,  and  manganese  ;  hardness  7  to  7.5, 
therefore  greater  than  that  of  quartz  or  rock-crystal. 

Garnet,  in  its  most  common  form  of  a  red  crystal, 
can  easily  be  recognized  by  its  ordinary  garnet  appear- 


COMMONER   BOCK-FORMING  MINERALS.         249 

ance ;  i.e.,  by  its  resemblance  to  the  stone  of  com- 
merce, which  it  is,  in  fact.  The  so-called  "  precious  " 
garnets  are  merely  the  clearer  varieties  which  permit 
of  cutting  for  gem-stone.  They  are  generally  of  the 
varieties  known  as  Pyrope  (a  magnesia  garnet)  and 
Almandite  (an  iron  garnet)  ;  the  Hessonite,  or  "  cinna- 
mon-stone "  (a  lime  garnet),  is  also  used  for  commercial 
purposes.  Among  the  other  forms  and  varieties  that 
may  be  mentioned  are  Grrossularite,  a  lime  garnet  of 
yellowish  or  greenish  (sometimes  brown  or  rose)  color, 
so-called  from  an  assumed  resemblance  to  the  goose- 
berry; and  Uvarovite,  a  chrome  garnet  of  a  beautiful 
emerald-green  color;  the  common  forms  of  gneiss  and 
schist  are  the  iron  garnets,  Almandite  and  Andradite. 

Tourmaline  is  a  common  accessory  mineral  in  gran- 
ites and  associated  rocks,  but  it  also  occurs  in  lime- 
stones and  arenaceous  rocks.  Its  usual  form  is  that  of 
a  glassy  prismatic  crystal,  with  three,  six,  or  nine  sides 
(or  rounded  in  such  a  way  as  to  obscure  the  sides),  of 
coal  blackness,  and  with  a  powdery  fracture,  much  like 
that  of  coal.  The  crystals  are  at  times  hardly  larger 
than  hair-lines,  and  are  then  frequently  grouped  in 
radial  clusters ;  at  other  times  they  are  of  almost  pon- 
derous proportions,  rivalling  some  of  the  largest  known. 
It  frequently  so  nearly  resembles  hornblende  as  to  be 
easily  mistaken  for  it ;  but  the  absence  of  cleavage,  the 
brittle,  coaly  fracture,  and  glassy  form  of  the  mineral 
ought  to  serve  to  distinguish  it.  In  quartz  masses, 
where  it  so  often  occurs,  it  frequently  shows  itself  to 
be  traversed  by  quartz  veins  or  partitions,  looking  as 
though  it  were  patched  up  of  superimposed  parts.  In 
chemical  composition  it  is  essentially  a  silicate  of  alu- 


250  THE  EARTH  AND  ITS   STORY. 

mina,  with  iron,  magnesia,  and  the  rare  element  boron ; 
lithia,  soda,  or  potash  may  also  be  present.  The  hard- 
ness is  7-7.5.  Tourmaline,  apart  from  its  more  com 
mon  black  form,  occurs  in  brown,  green,  yellow,  blue, 
and  pink,  and  sometimes  in  combinations  of  green  and 
pink ;  the  pink  variety,  known  as  MubcUite,  contains 
lithia. 

Fluorite,  or  Fluor-Spar,  a  compound  of  calcium  and 
fluorine,  is  one  of  the  most  beautiful  of  minerals ;  and 
its  cubical  crystals  of  yellow,  green,  blue,  purple,  red, 
and  brown  —  also  colorless  —  can  easily  be  distinguished 
either  by  form  or  moderate  hardness,  4,  from  those  of 
calcite  and  quartz.  It  also  occurs  massive,  like  calcite, 
and  in  one  of  its  ornamental  forms  constitutes  the 
beautiful  Derbyshire  spar.  Fluorite  possesses  the  prop- 
erty known  as  fluorescence,  —  emitting  a  peculiar  blue 
light  of  its  own,  —  and  when  fragmented  and  moder- 
ately heated  becomes  phosphorescent.  Hydrofluoric 
acid,  which  is  so  extensively  used  in  the  arts  for 
etching  glass,  is  obtained  from  it. 

Apatite,  a  compound  of  phosphoric  acid  and  lime 
(phosphate  of  lime),  is  a  widely  distributed  mineral, 
and  is  eagerly  sought  after  for  its  beautiful  hexagonal 
crystals  of  yellow,  green,  blue,  red,  brown,  and  black ; 
some  of  these  are  quite  clear  and  colorless,  but  ordi- 
narily they  are  opaque,  and  with  glassy  or  resinous 
lustre.  Exceptionally,  as  in  parts  of  Canada,  the  crys- 
tals may  be  as  large  as  a  nail-keg.  The  hardness  is  5, 
and  therefore  below  both  feldspar  and  quartz.  It  is 
largely  associated  with  the  crystalline  rocks,  where, 
either  in  its  crystalline  form  or  as  amorphous  masses, 
it  fills  in  veins,  streaks,  and  pockets.  It  has  been 


COMMONER   ROCK-FORMING  MINERALS.        251 

extensively  mined  for  the  fertilizing  phosphate  which 
it  yields  under  proper  treatment;  and  from  it  also  is 
obtained  some  of  the  phosphorus  of  commerce. 

Beryl  is  not  a  rare  accessory  component  of  the  gra- 
nitic rocks.  It  occurs  usually  in  hexagonal  crystals, 
abruptly  terminated  or  truncated,  of  a  green  color, 
some  of  them  very  much  resembling  the  more  glassy 
forms  of  green  apatite,  and  at  times  difficult  to  distin- 
guish from  them.  The  hardness  is,  however,  above 
that  of  quartz,  7.5.  As  with  apatite,  the  crystals  are 
often  of  ponderous  proportions,  some  of  the  New  Hamp- 
shire specimens  being  as  large  as  a  barrel.  The  clear 
and  transparent  varieties  of  beryl  are  among  the  most 
highly  prized  of  gem-stones;  such  are  Aquamarine,  of 
a  clear  mountain-green  color,  and  Emerald,  of  a  deep 
emerald-green.  Yellow  and  pink  varieties  are  also 
known.  Beryl  is  in  composition  a  silicate  of  alumina 
and  glucina ;  the  element  glucinum,  or  beryllium,  in 
combination  with  aluminic  acid,  forms  the  gem  min- 
erals Chrysoberyl  (with  the  variety  known  as  "cat's- 
eye  ")  and  Alexandrite. 

Topaz  is  ordinarily  considered  one  of  the  gem-stones ; 
and,  like  most  of  these,  its  association  is  with  the  crys- 
talline rocks,  granites,  and  gneisses.  It  occurs  in  pris- 
matic crystals,  frequently  of  large  size,  and  colorless, 
or  of  shades  of  white,  yellow,  blue,  and  pink.  Most  of 
the  pink  coloring  seen  in  these  stones  has  been  artifi- 
cially brought  about.  Topaz  is  one  of  the  hardest  of 
minerals,  rating  as  8  ;  but  it  breaks  readily  in  a  direc- 
tion across  the  crystal  prism.  In  composition  it  is  a 
compound  of  silica  and  alumina  (silicate  of  alumina), 
with  the  rare  element  fluorine  added. 


252  THE  EARTH  AND  ITS   STORY. 

Cryolite  is  a  rare  mineral,  occurring  in  quantity  only 
in  South  Greenland ;  but  it  has  come  into  prominence 
through  its  association  with  the  making  of  soda  salts 
and  the  extraction  of  the  much-coveted  aluminium 
metal.  It  is  an  attractive  white  (sometimes  reddish) 
mineral,  and  receives  its  name  cryolite,  or  ice-stone, 
from  an  assumed  resemblance  between  it  and  blocks 
of  ice  ;  it  fuses  readily,  and  in  thin  pieces  will  burn 
even  in  a  candle-flame.  In  composition  it  is  fluorine, 
sodium,  and  aluminium. 

Turquoise  is  readily  distinguished  as  a  gem-stone  by 
its  robin's-egg-blue  color. 

It  occurs  only  in  massive  form  (not  in  crystals), 
filling  cavities  and  seams  in  volcanic  rock;  the  best 
forms  come  from  Persia  and  New  Mexico.  It  is  a 
watery  or  hydrous  compound  of  phosphoric  acid  and 
aluminium  (phosphate  of  alumina). 

Ruby,  as  the  gem-stone,  is  an  oxide  of  aluminium, 
and  properly  only  a  variety  of  the  mineral  corundum ; 
as  such,  it  should  be  distinguished  from  Balas-ruby,  or 
Spinel,  which  is  an  aluminate  of  magnesia.  As  has 
already  been  described  under  corundum,  the  bright  blue 
variety  is  known  as  /Sapphire,  the  purple  as  Oriental 
Amethyst,  and  the  yellow  as  Oriental  Topaz.  The 
finest  true  rubies  still  come  from  the  Orient,  —  Siam, 
Burmah,  and  elsewhere  in  the  East  Indies,  —  and  the 
sapphires  from  Ceylon.  These  all  have  a  hardness 
next  to  diamond,  9,  and  consequently  stand  second  in 
the  scale  of  greatest  hardness. 

Diamond  usually  occurs  in  the  form  of  small  octa- 
hedral crystals,  but  sometimes,  as  in  the  case  of  the 
famous  crown  diamonds,  as  large  as  a  robin-egg,  or 


COMMONER  ROCK-FORMING  MINERALS.        253 

even  considerably  larger.  Its  distinctive  qualities  — 
such  as  brilliancy,  extreme  hardness,  infusibility,  and 
insolubility  —  are  well  known ;  when  highly  heated,  it 
slowly  consumes,  and  disappears  as  carbonic  acid  gas. 
In  composition  it  is  pure  carbon.  Its  most  highly 
prized  varieties  are  colorless  and  clear  as  water  (hence, 
"of  the  first  water")  ;  but  gems  are  not  uncommon  in 
pale  shades  of  yellow,  green,  pink,  and  blue.  The 
famous  "  Hope "  diamond  has  a  decided  blue  color; 
less  valuable  as  gem-stones  —  in  fact,  scarcely  valuable 
except  as  curiosities  —  are  the  black  diamonds.  Much 
of  the  impure  dark  variety  (known  as  Carbonado),  and 
the  fragmental  pieces  that  are  not  serviceable  for  gem- 
stones,  are  used  in  the  form  of  diamond  powder  (borf) 
for  polishing  and  cutting  purposes  (diamond-drilling). 
The  most  important  diamond-producing  countries  of 
the  world  are  India,  Brazil,  and  South  Africa ;  at  the 
present  time,  South  Africa  far  surpasses  in  output  the 
combined  outputs  of  all  the  other  regions  of  the  earth's 
surface.  Several  tons  of  the  precious  stone  have  actu- 
ally been  obtained  from  the  Kimberley  mines,  along  the 
Vaal  River,  during  the  period  of  the  last  quarter  of 
a  century.  The  diamond  is  commonly  found  in  gravel 
deposits,  or  in  rocks  formed  of  their  consolidation,  and 
in  a  peculiar  blue  earth  or  blue  rock  known  as  Kim- 
berleyite,  or  modified  Peridotite ;  little  is  known  as  to 
its  origin  or  genesis.  Among  the  most  famous  stones 
are  the  " Koh-i-noor"  of  the  English  crown  jewels,  the 
"  Orlov  "  of  Russia,  the  "  Florentine  "  of  Austria,  and 
the  " Regent,"  or  "Pitt,"  now  in  the  Louvre  of  Paris. 
All  of  these  have  been  far  surpassed  in  size  by  recent 
finds  in  the  Orange  Free  State,  South  Africa, 


TEACHERS'   REFERENCES. 


CHAPTER  I.  —  State  the  general  changes  which  rock-masses 
undergo  ;  the  effect  of  water-freezing  ;  the  influence  of  tempera- 
ture alternations.  Define  the  nature  of  internal  disintegration. 
Give  the  two  distinctive  methods  of  rock-destruction.  What  is 
understood  by  "  weathering  "  ?  State  how  desert  sands  are  formed, 
and  give  the  reason  for  their  accumulation  in  great  quantity.  Indi- 
cate the  general  course  which  the  materials  resulting  from  terrestrial 
destruction  take,  and  note  their  special  distribution. 

CHAPTER  II.  —  Define  a  sandstone,  a  conglomerate,  and  indi- 
cate whence  the  materials  of  their  construction  have  been  obtained. 
What  is  the  nature  of  a  binding  cement  ?  Describe  accurately  a 
limestone,  and  enumerate  a  few  typical  forms  of  such  rock  ;  give  its 
chemical  and  its  organic  structure.  How  does  marble  differ  from 
ordinary  limestone  ?  What  is  coquina  ?  Give  the  composition  of 
chalk,  and  indicate  its  relations  to  the  oceanic  or  Globigerina  ooze  ; 
define  the  latter. 

Define  flags,  shales,  and  slates  ;  indicate  their  points  of  agree- 
ment and  of  difference,  and  point  out  their  relations  to  modern  mud 
and  soil.  What  special  marks  have  been  impressed  upon  them  ?  — 
ripples,  raindrop  impressions,  etc.  Give  the  construction  and  com- 
position of  granite  and  syenite,  indicating  the  mineral  constituents 
of  each.  Enumerate  some  varieties  of  granite  and  granitic  rocks. 
State  the  origin  of  granite.  Give  a  broad  classification  of  the  rocks 
of  the  earth,  defining  the  terms  igneous,  aqueous,  and  plutonic. 
Describe  gneiss,  and  point  out  some  of  the  characters  wherein  it 
agrees  with,  and  differs  from,  granite.  What  is  understood  by 
"foliation"  ?  State  the  origin  of  gneiss,  and  give  an  explanation 
of  the  terms  "  metamorphic  "  and  "metamorphism."  Describe  the 
term  "schist,"  and  enumerate  some  of  the  schistose  rocks, — mica 
schist,  hornblende  schist,  chlorite,  —  giving  their  general  construc- 
tion. 

CHAPTER  III.  —  Give  some  ready  means  for  determining  in  the 
field  such  rocks  as  sandstone,  limestone,  shale,  granite,  etc,  What 

254 


TEACHERS'   REFERENCES.  255 

is  the  significance  of  ancient  ripple-marks,  raindrop  impressions, 
and  footprints?  Explain  the  terms  "strata,"  "stratified,"  and 
"  sedimentary,"  and  point  out  their  significance  in  connection  with 
the  building  up  of  rock-masses.  What  is  the  normal  position  in 
which  rock-masses  are  deposited  ? 

How  is  a  departure  from  the  normal  horizontal  position  brought 
about  ?  Explain  rock-folding,  and  point  out  its  relation  to  a  definite 
condition  of  our  planet.  Represent  the  different  positions  occupied 
by  rock-masses  ;  define  the  term  "dip,"  giving  a  practical  illustra- 
tion of  its  meaning  by  folding  a  piece  of  paper  to  represent  it. 

CHAPTER  I Y.  —  What  first  characteristics  are  taught  by  moun- 
tain regions  ?  Illustrate  the  method  of  the  making  of  certain 
mountains  and  mountain  chains.  What  is  understood  by  a  "folded 
mountain  "  ?  Clearly  point  out  the  relations  existing  between 
mountain  backbones  and  original  "  longitudinal "  valleys.  Define 
the  terms  "  strike,"  "  anticline,"  and  "  syncline,"  and  represent 
these  structures  through  the  folding  of  a  piece  of  paper.  Indicate 
some  of  the  complexities  of  mountain  structure.  What  is  under- 
stood by  mountain  travel  or  "shearing"?  Explain  the  nature  of 
dislocations  and  "  faults."  Give  your  understanding  of  the  section- 
ing up  or  dismemberment  of  the  earth's  crust,  defining  the  features 
known  as  "  fallen  troughs  "  and  "  continental  buttresses  "  (or 
horsts),  and  illustrating  these  by  citations  of  structure  obtained 
from  different  continental  areas.  Indicate  the  relations  existing 
between  crustal  breakages  and  mountain-making. 

Give  by  name  such  mountains  as  define  the  terms  "old"  and 
"  new "  mountain,  etc.  Describe  the  work  of  the  atmospheric 
waters,  and  point  out  its  relation  to  the  making  of  scenery.  What 
are  earth-pillars  and  "  buttes,"  and  how  do  such  topographic  fea- 
tures originate  ?  Cite  some  localities  of  their  occurrence.  Explain 
what  is  meant  by  "aqueous  erosion."  Give  the  relation  of  ravines 
and  gorges  to  water-action.  Define  the  terms  "base-level  of  ero- 
sion," and  the  structural  feature  known  as  "  peneplain."  Describe 
a  canon,  and  indicate  the  region  where  canons  are  most  largely 
developed. 

Clearly  define  the  terms  "old"  and  "new"  as  pertaining  to  the 
features  in  a  landscape.  Explain  the  nature  of  valleys  in  a  com- 
plicated mountain  region,  pointing  out  the  changes  in  position 
and  relation  which  they  undergo.  How  are  "transverse"  valleys 
formed?  Explain  the  nature  of  "mountain  (or  "water")  gaps," 
and  cite  localities  where  such  gaps  are  found.  Describe  the  nature 


256  ,  THE  EARTH  AND  ITS   STORY. 

of  river-terraces,  and  point  out  their  relation  to  the  course  of  a 
river  and  to  its  flood-plain.  What  relation  does  a  lake  basin  bear 
to  the  stream  that  discharges  into  it  ?  Define  the  process  of  silting, 
and  point  out  the  ultimate  result  that  is  obtained  in  this  process. 
Give  the  relation  existing  between  many  meadow-lands  and  lake 
basins.  Give  the  origin  of  lake  basins,  with  special  reference  to  the 
work  of  glaciers.  What  are  "  crater  lakes  "  ?  Explain  the  land- 
locking  of  certain  lakes.  Interpret  the  nature  of  desiccating  lakes, 
and  the  condition  of  salinity  that  accompanies  the  contraction. 
Illustrate  the  positions  of  some  of  the  ancient  lakes  of  the  North 
American  continent,  pointing  out  their  relation  to  existing  bodies 
of  water.  Name  some  of  the  lakes  of  the  Great  Basin.  Analyze 
the  scenery  of  lake-shores. 

CHAPTER  Y.  —  Describe  the  position  of  the  snows  on  the  Alps. 
What  is  understood  by  the  "snow-line,"  and  where  does  it  lie  in 
different  parts  of  the  earth  ?  State  what  becomes  of  the  mountain 
snows,  and  give  some  approximation  to  the  thickness  in  which  it 
occurs.  Describe  generally  a  Swiss  glacier.  What  do  the  "  cre- 
vasses" and  "seracs"  represent?  Define  a  "moraine,"  and  explain 
the  nature  of  glacial  "  strice  "  and  "  erratics."  Distinguish  between 
the  "lateral"  and  "terminal"  moraines.  Give  a  description  of 
the  general  aspect  of  a  glacier.  Indicate  the  special  characteristics 
of  glacial  ice.  What  are  "  gletscherkorn"  and  "neve"  (or  "./Srn")? 
Describe  the  origin  and  method  of  formation  of  a  glacier.  What  is 
understood  by  the  "  neve-  (or  "Jirn-")  basin,"  and  where  is  it  found  ? 
What  are  "compound  glaciers  "  ?  Define  the  "medial  "  moraine. 

CHAPTER  VI. — Describe  the  motion  or  "flow"  of  a  glacier, 
giving  some  of  its  special  characteristics.  What  is  understood  by 
the  term  "  regelation "  ?  Give  some  illustrations  of  the  rate  of 
movement  of  certain  glaciers,  and  the  conditions  which  determine 
this  movement.  Describe  the  mechanical  work  that  is  being  per- 
formed by  a  glacier  —  the  scouring  and  polishing  of  rocks.  Define 
the  "  roches-moutonnees."  Indicate  the  possible  relation  existing 
between  glacial  scour  and  the  making  of  rock  lake  basins.  What 
is  understood  by  "  drift,"  and  what  relation  does  it  bear  to  glacial 
work?  What  is  "ground-moraine"  (or  "till"),  and  what  other 
special  features  are  associated  with  the  glacial  landscape  ("drum- 
lins,"  "kames,"  "eskers")  ? 

Explain  the  condition  of  the  "retreat  "  of  glaciers.  How  does  a 
glacier  in  recession  conform  to  its  terminal  moraine  ?  Give  the  dis- 
tribution and  dimensions  of  existing  glaciers,  Enumerate  some  of 


TEACHERS'   REFERENCES.  257 

the  largest  glaciers  of  the  world,  and  give  an  approximation  to  the 
possible  thickness  of  ice  out  of  which  they  are  composed.  Give 
the  evidences  of  past  continental  glaciation.  Define  the  "  Great 
Ice  Age."  Illustrate  by  means  of  a  map  the  direction  of  movement 
of  the  ice  of  the  Great  Ice  Age  (or  "  Glacial  Period").  State  the 
probable  points  of  departure  of  the  ice  in  both  Europe  and  North 
America.  Define  the  "great  terminal  moraine,"  and  point  out 
some  of  its  relations  to  the  lakes  which  are  now  found  within  its 
boundaries.  What  is  understood  by  the  morainic  "lobes"  ?  What 
may  have  been  the  cause  of  the  Great  Ice  Age,  and  what  the  meas- 
ure of  time  that  has  intervened  since  its  disappearance  ? 

CHAPTER  VII.  —  Explain  the  nature  of  mineral  waters,  and  cite 
some  of  their  distinctive  types.  On  what  condition  is  the  quantity 
of  the  mineral  salts  largely  dependent  ?  Describe  the  methods  of 
the  formation  of  caves,  and  name  some  of  the  largest  and  best- 
known  caves.  What  are  "  cave-rifts  "  and  "  bone-caves  "  ?  Mention 
some  of  the  most  noted  hone-caves  of  the  world,  and  enumerate  the 
animal  forms  that  are  most  largely  associated  with  them.  Explain 
the  nature  of  "natural  bridges."  Define  the  terms  "stalactite," 
"stalagmite,"  and  "  stalagmitic  crust."  What  is  an  "ice-cave," 
and  under  what  special  conditions  may  its  deposits  of  ice  have 
accumulated  ? 

Explain  the  nature  of  "  hot  springs,"  and  approximate  the 
temperatures  which  mark  some  of  their  waters.  State  the  rela- 
tion existing  between  high  water-temperatures  and  the  internal 
temperature  of  the  earth.  What  is  a  geyser,  and  how  does  it  most 
markedly  differ  from  the  ordinary  hot  springs  ?  Explain  clearly  the 
parts  of  a  geyser  —  the  geyser  "cone,"  vertical  conduit,  top-basin, 
etc.  Enumerate  some  of  the  best-known  geysers,  the  localities  of 
their  occurrence,  and  the  dimensions  of  the  special  parts.  What  is 
understood  by  siliceous  and  calcareous  "sinter"  ?  Mention  some 
of  the  most  famous  geyser  deposits. 

CHAPTER  VIII.  — Give  the  configuration  of  the  oceanic  trough. 
State  its  probable  origin,  and  give  the  evidence  in  favor  of  consider- 
ing it  an  area  of  weakness  in  the  original  crust.  To  what  extent 
are  the  continents  and  oceans  permanent  or  non-permanent  in 
position  ?  Cite  some  facts  indicating  or  proving  the  disruption  of 
continental  masses.  Give  the  configuration  of  the  Atlantic  basin, 
with  a  statement  of  its  depths,  and  the  relation  of  its  several  pro- 
jecting ridges.  What  is  understood  by  "  inconstancy  of  the  ocean- 
level,"  and  to  what  degree  may  this  inconstancy  be  developed? 


258  THE  EARTH  AND  ITS  STORY. 

Define  the  nature  of  "oceanic  transgressions"  and  "oceanic  reces- 
sions." Define  the  nature  of  a  "drowned  land,"  and  of  "  drowned 
waters."  Illustrate  the  latter  condition  by  reference  to  some  of  the 
American  rivers. 

Analyze  the  conditions  that  are  taught  by  the  terms  "  submer- 
gence," "positive  subsidence,"  and  "apparent  subsidence."  State 
the  nature  of  fjords,  and  point  out  their  relations  to  the  valleys 
of  the  land-surface.  What  are  "ocean  terraces,"  and  what  broad 
fact  do  they  teach  ?  Describe  the  wear  of  the  coast-line,  and  name 
some  of  the  features  that  are  incised  into  it  as  the  result  of  the 
oceanic  distruction — "ovens,"  "blow-holes,"  etc.  What  is  the 
"  plain  of  marine  denudation,"  and  in  what  respect  does  it  differ 
from  the  "peneplain"  ?  Illustrate  the  breaking  up  of  coast-lines 
through  the  encroaches  of  the  sea,  citing  prominent  instances  where 
a  dismemberment  of  the  land  has  been  brought  about.  Give  some 
instances  of  the  destroying  power  of  the  sea.  What  do  we  under- 
stand by  the  "  sediment  "  and  "  sediment  discharge  "  of  rivers  ? 
Indicate  how  the  sediment  discharge  of  a  river  may  be  measured 
or  determined,  and  point  out  what  relation  this  sediment  bears  to 
the  drainage-basin  of  a  river.  Give  an  approximate  rate  of  "  denu- 
dation "  of  the  land-surface.  In  what  way  does  the  sediment 
carried  out  by  rivers  help  to  make  new  land  ?  How  does  the  wear 
and  tear  of  the  coast-line  help  to  make  new  land  ?  Cite  some 
instances  of  the  encroaches  of  the  land  upon  the  sea. 

CHAPTER  IX.  —  State  the  probable  condition  of  the  earth's 
interior.  Give  the  approximate  rate  of  increase  of  temperature  in 
the  interior,  and  indicate  what  influence,  if  any,  this  temperature 
has  upon  climate  or  the  surface  of  the  globe.  What  effect  has 
pressure  upon  the  liquefaction  of  rock-masses  ?  What  are  the 
assumed  "pockets  of  molten  material"?  Give  the  density  or 
weight  of  the  earth,  with  a  statement  as  to  the  possible  condition 
or  character  of  the  rock-masses  of  the  deeper  interior. 

CHAPTER  X.  —  Describe  the  general  aspects  of  a  volcano,  clearly 
defining  its  special  parts,  such  as  the  cone,  crater,  conelet,  etc. 
Describe  the  operations  of  a  volcano,  and  detail  the  changes  that 
are  brought  about  by  work  in  progress.  What  is  understood  by  the 
volcanic  neck  or  "funnel"  ?  What  is  understood  by  the  "smok- 
ing" of  volcanoes?  Detail  the  inner  construction  of  a  volcanic 
mountain.  Enumerate  the  kinds  of  materials  that  are  discharged 
by  a  volcano,  and  indicate  their  relations  to  the  building  up  of  the 
mountain.  Give  the  dimensions  of  some  of  the  largest  volcanoes, 


TEACHERS'  REFERENCES.          259 

and  the  proportional  amounts  of  material  that  they  throw  out. 
Specify  the  characters  of  "  composite,"  "cinder,"  and  "ash"  cones. 
Define  "lava,"  "scoria,"  "ash,"  and  "tuff." 

Explain  the  working  activity  of  the  volcanic  mountain.  What 
is  understood  by  the  condition  of  being  "  extinct,"  and  what  changes 
or  new  structures  in  the  mountain  accompany  extinction  ?  Indicate 
the  difference  between  a  paroxysmal  and  a  non-paroxysmal  erup- 
tion. Explain  the  nature  of  the  "  crater-ring."  State  the  methods 
of  the  decapitation  of  a  volcanic  mountain.  What  is  meant  by  the 
"  shifting  "  of  the  points  of  activity  ?  Define  the  nature  of  "  para- 
sitic cones"  and  of  volcanic  "dikes."  Give  the  after-history  of 
a  volcano.  Give  the  nature  of  "  crater-lakes,"  and  mention  some 
of  the  better-known  water-basins  having  their  character.  Explain 
what  is  a  volcanic  "neck"  or  "plug." 

State  the  possible  cause  of  eruption.  Describe  the  nature  of 
fissure  eruptions,  and  name  some  of  the  localities  on  the  earth's 
surface  where  such  eruptions  have  taken  place.  Explain  the  mean- 
ing of  "trap."  Define  a  "dike."  Explain  the  nature  of  "lacco- 
lites,"  and  state  where  such  are  found. 

CHAPTER  XI.  —  Give  the  distribution  of  modern  volcanoes,  with 
reference  to  the  two  main  belts  of  their  occurrence.  What  charac- 
teristic in  their  distribution  is  specially  emphasized.  Enumerate 
some  of  the  loftiest  and  most  active  cones.  Define  an  earthquake, 
and  indicate  some  of  the  ways  in  which  earthquakes  are  produced. 
What  relation  exists  between  earthquake  and  volcanic  phenomena  ? 
Illustrate  the  relation  existing  between  land-slipping  and  earth- 
quakes. How  does  the  abstraction  of  material  from  the  interior  of 
the  earth  affect  the  surface?  Give  the  probable  depth  of  origin 
of  an  earthquake,  and  state  the  possible  extent  to  which  the  earth- 
quake impulse  may  be  propagated.  What  is  understood  by  the 
"earthquake-wave"?  Describe  the  passage  of  the  earthquake- 
wave,  and  indicate  some  of  the  conditions  by  which  it  is  determined 
or  regulated.  What  is  the  extent  or  intensity  of  the  earthquake 
movement  ?  Cite  instances  where  permanent  land-displacements 
have  followed  earthquakes.  Give  the  nature  of  the  oceanic  or 
"tidal  wave  "  which  is  frequently  associated  with  earthquakes.  Give 
the  velocities  with  which  the  terrestrial  and  oceanic  impulses  are 
transmitted. 

CHAPTER  XII.  —  Describe  the  aspects  of  a  coral  reef.  Describe 
the  making  of  .coral  land,  and  give  the  special  conditions  which 
govern  the  life  and  distribution  of  the  reef-building  coral.  What 


260  THE  EARTH  AND  ITS   STORY. 

do  we  understand  by  the  wind-drift  or  seolian  character  of  coral 
sand  ?  Name  the  different  kinds  of  coral  islands  and  reefs,  — 
"atolls,"  "barrier-reefs,"  "f ringing-reefs," — and  clearly  indicate 
their  differences  and  similarities.  Define  the  parts  of  an  atoll,  — 
"lagoon,"  "ring"  or  collar,  etc.  Explain  the  occurrence  of  reef- 
structures  in  the  deeper  waters  of  the  ocean,  with  special  reference 
to  the  "  subsidence  theory"  of  coral  formations.  What  may  be  the 
probable  thickness  of  the  coral-made  rock  ?  Explain  the  nature  of 
organically  constructed  oceanic  "banks,"  or  "platforms,"  with  ref- 
erence to  the  physics  of  certain  reef-structures.  Explain  the 
nature  and  condition  of  existence  of  "  elevated  reefs."  Give  the  dis- 
tribution of  modern  reefs,  citing  some  of  the  best-known  examples 
of  their  occurrence.  Give  the  distribution  of  some  ancient  reefs. 

CHAPTER  XIII.  —  Define  a  fossil,  and  cite  examples  from  both 
the  organic  and  the  inorganic  world.  State  the  manner  of  occur- 
rence of  fossils,  specially  defining  the  conditions  known  as  "casts," 
"  moulds,"  and  "  impressions."  What  do  we  know  of  the  preserva- 
tion of  fossils  and  of  their  special  markings  (color,  etc.)  ?  What  is 
understood  by  "progression  in  structure"  in  the  organic  chain? 
Give  a  synoptical  review  of  the  order  of  occurrence  of  some  of  the 
principal  animal  types.  What  is  understood  by  the  "  doctrine 
of  evolution  "  as  pertaining  to  organic  forms  ?  Define  the  "  time- 
standard"  of  geological  history.  Explain  "variation"  and  "ex- 
tinction" in  animal  forms.  What  is  understood  by  "natural 
selection  "  ?  What  is  the  "  struggle  for  existence  "  ?  Define  "  dis- 
appearance "  and  "reappearance."  Define  a  geological  "horizon." 
What  is  a  leading-  or  "  type-fossil "  ? 

Give  (from  the  table)  the  names  of  the  main  "epochs,"  or 
"  formations "  belonging  to  these  epochs,  which  are  recognized 
by  geologists.  Enumerate  some  of  the  more  distinctive  fossils  that 
belong  to  each  of  these.  About  where  do  the  fishes  make  their 
appearance — the  amphibians,  reptiles,  birds,  mammals?  Where 
does  man  belong  ?  How  far  back  in  time  does  a  land-vegetation 
extend  ?  What  were  some  of  the  earliest  insects  ? 

Define  the  different  kinds  of  fossils  —  marine,  terrestrial,  and 
fresh-water,  and  state  their  mutual  relations  to  one  another  (or 
the  probable  lines  of  their  origin).  Briefly  characterize,  from  a 
faunal  aspect,  the  faunas  of  the  different  periods,  —  Cambrian, 
Silurian,  Devonian,  etc., — and  emphasize  their  relations  to  one 
another  from  the  point  of  view  of  the  evolutionist  and  of  pro- 
gressive development. 


TEACHERS*   REFERENCES.  261 

CHAPTER  XIY.  —  Give  the  organization  of  some  leading  groups 
of  fossils,  —  "  Foraminifera,"  corals,  "  trilobites,"  "crinoids,"  etc. 

CHAPTER  XV.  —  Give  your  knowledge  regarding  fossil  fishes, 
reptiles,  birds,  and  mammals.  Define  the  nature  of  the  "Ptero- 
dactyls," of  "  Archaeopteryx."  What  were  the  "  Odontornithes  "  ? 
Outline  the  order  of  appearance  and  succession  of  the  Mammalia. 
Give  the  broad  origin  of  the  existing  faunas  of  the  globe.  What  is 
understood  by  "ancestral  forms  "  ?  and  cite  an  instance  of  modifica- 
tion through  descent.  State  something  about  the  antiquity  of  man, 
and  of  his  association  with  the  mammoth  and  mastodon.  Where 
have  ancient  remains  of  man  been  found,  and  what  do  they  indi- 
cate ? 

CHAPTER  XYI. — Give  the  physiognomy  of  some  of  the  conti- 
nental areas  of  the  globe.  What  relation  exists  between  mountain 
lines  and  seashores  ?  Define  the  different  types  of  coast-line.  Give 
the  physiognomy  of  mountain  masses,  in  their  aspects  of  ridges, 
valleys,  general  contours  (slope,  etc.),  age,  and  scenery.  Define  the 
terms  that  are  frequently  applied  to  different  parts  of  a  mountain,  — 
"col"  (or  "Juch")  "arete,"  "aiguilles,"  "couloir,"  "massif," 
etc.  Define  the  "anticlinal,"  "synclinal,"  and  "  monoclinal " 
mountain.  What  is  understood  by  the  term  "fault  block"? 

Give  the  physiognomy  of  plateaus  and  of  "  plateau  mountains." 
Where  do  examples  of  the  latter  occur  ?  Explain  the  difference 
between  the  "mountain  plateau"  and  the  "continental  plateau." 
Give  illustrations  of  both  structures.  Describe  the  nature  of  the 
Greenland  and  Mexican  plateaus.  Give  the  physiognomy  of  valleys, 
clearly  characterizing  "plains"  and  valleys  proper,  and  the  differ- 
ent modifications  of  the  latter.  Define  the  V-shaped  valley,  the 
U-shaped  valley,  and  the  glacial  valley.  Give  the  physiognomy  of 
the  coast-line,  and  state  the  relation  existing  between  coast-lines 
and  mountain  chains.  What  do  open  and  closed  coast-lines  specifi- 
cally indicate  ?  What  do  "hooks,"  barriers,"  and  detached  head- 
lands and  rocks  signify  ? 

Give  the  physiognomy  of  rock-masses  —  their  positions  in  the 
field  and  relations  to  one  another.  Define  the  terms  "anticline," 
"syncline,"  "monocline,"  "dip,"  "strike";  how  are  the  condi- 
tions of  these  structures  brought  about  ?  What  is  understood  by 
"unconformity"?  What  is  a  geological  "break"?  State  some 
of  the  special  characters  impressed  upon  rock-masses.  Explain 
"current-bedding"  and  " flow-and-plunge  "  structure. 

CHAPTER  XVII.  —  Give  the  characters  and  modes  of  occurrence 


262  THE  EARTH  AND  ITS   STORY. 

of  some  of  the  more  useful  metals  and  minerals,  such  as  gold,  silver, 
copper,  lead,  iron,  etc.  Enumerate  the  most  serviceable  ores  of  the 
principal  metals.  Describe  the  method  of  coal  formation,  and  give 
the  condition  of  the  United  States  (in  part)  during  the  making 
of  its  coal.  Name  some  of  the  most  distinctive  plants  of  the 
coal-period.  Give  the  areas  of  the  principal  coal-fields  of  the  world. 
Give  the  production  of  coal.  Enumerate  the  principal  varieties 
of  coal,  and  state  their  characteristics.  Define  petroleum  and 
"natural  gas."  State  something  about  the  production  of  these 
substances.  What  is  "bitumen"  or  "asphalt"  ? 

CHAPTER  XVIII.  —  Give  some  of  the  special  characteristics  and 
requirements  of  building-stones.  Enumerate  some  of  the  better 
varieties  or  classes  of  such.  What  are  some  of  the  deficiencies  in 
building-stones  ?  Give  your  knowledge  regarding  "flagging-stones," 
roofing-slates,  and  "tile-stones."  Define  and  characterize  clays  and 
soils.  What  is  understood  by  the  terms  "glacial  drift,"  "bowlder- 
clay,"  "till,"  etc?  What  are  "marls"  and  "  loams  "?  Describe 
the  "greensands"  of  the  Atlantic  slope  of  the  United  States. 
Enumerate  some  of  the  most  efficient  fertilizers  —  lime,  guano, 
phosphates.  Where  do  some  of  the  richest  phosphate  beds  occur  ? 
Define  a  "bone-bed." 

CHAPTER  XIX. — Name  the  most  important  rock-forming  min- 
erals, and  state  how  they  occur,  and  what  special  rocks  they  form. 
Enumerate  the  more  important  varieties  of  quartz,  and  give  their 
chemical  composition  and  distinctive  characters.  Give  the  general 
characters  and  composition  of  calcite,  feldspar,  hornblende,  mica, 
etc.  What  is  the  "  scale  of  hardness,"  and  how  is  it  constituted  ? 
Name  and  briefly  define  some  of  the  more  important  gem-stones,  as 
emerald,  diamond,  ruby,  etc.  Mention  other  accessory  minerals  of 
rock-masses. 


INDEX. 


Actinollte,  247. 
Adularia,  245. 
^Epyornis,  179. 
Agate,  243. 
Albite,  245. 
Almandite,  249. 
Aluminium,  222» 
Amalgam,  221. 
Amazon-stone,  245. 
Amethyst,  243. 
Ammonites,  171. 
Anticlines,  45. 
Antimony,  214. 
Apatite,  250. 
Aquamarine,  251. 
Aqueous  rocks,  33. 
Aragonite,  244. 
Archaean,  155. 
Archseopteryx,  177. 
Argentite,  209. 
Arsenic,  214. 
Asbestus,  247. 
Asphaltum,  231. 
Atlantic  basin,  98. 
Atoll,  142,  145. 
Augite,  248. 
Azoic,  155. 
Azurite,  211. 

Baculites,  173. 
Barrier-reef,  142. 
Basalt,  122. 
Base-level,  53. 
Bats,  fossil,  180. 
Bear,  fossil,  181. 
Beauxite,  223. 
Belemnites,  173. 
Beryl,  251. 


Birds,  fossil,  178. 
Bitumen,  231. 
Bone-caves,  89. 
Bornite,  210. 
Bort,  253. 
Brachiopods,  169. 
Breaks,  geological,  204. 
Brontosaurus,  176. 
Bronzite,  248. 
Building-stones,  232. 
Buttresses,  47. 

Cainozoic,  155. 

Calamine,  212. 

Calcite,  243. 

Cambrian,  155. 

Camerasaurus,  176. 

Canons,  53. 

Carbonado,  253. 

Carboniferous,  155. 

Carnelian,  243. 

Carnivores,  fossil,  180. 

Cassiterite,  212. 

Cat,  fossil,  180. 

Cat's  Eye,  243. 

Caves,  formation  of,  88 ;  bone, 

ice,  90. 

Cephalaspis,  175. 
Chalcedony,  243. 
Chalcopyrite,  210. 
Chalk,  composition  of,  27, 155. 
Chert,  243. 
Chromite,  219. 
Chrysoberyl,  251. 
Chrysoprase,  243. 
Cinnabar,  221. 
Cinnamon-stone,  249. 
Clays,  238. 


263 


264 


THE  EARTH  AND  ITS   STORY. 


Coal,  226;  coal-plants,  228;  varie- 
ties of  coal,  229. 

Coast-lines,  relation  of,  to  conti- 
nents, 187;  general  physiog- 
nomy of,  199. 

Cones,  volcanic,  121 ;  parasitic,  124. 

Condylarthra,  180. 

Conglomerates,  21. 

Continents,  permanency  of,  96;  dis- 
ruption of,  97 ;  physiognomy  of, 
185. 

Copper,  209. 

Corals,  tabulate,  etc.,  166. 

Coral-reefs,  aspects  of,  138;  mak- 
ing of,  140 ;  kinds  of,  142 ;  for- 
mation of,  143;  elevated,  146; 
distribution  of,  147;  ancient, 
148. 

Corundum,  223. 

Creodonta,  180. 

Cretaceous,  155. 

Crinoids,  168. 

Crioceras;  173. 

Crocoite,  214. 

Crust,  breakages  in,  49. 

Cryolite,  223,  252. 

Cuprite,  210. 

Current-bedding,  206. 

Dendrite,  220. 

Deserts  and  desert-sands,  17. 

Devonian,  155. 

Diallage,  248. 

Diamond,  252. 

Dike,  volcanic,  129.- 

Dinichthys,  175. 

Dinoceras,  180. 

Dinornis,  178. 

Dinosauria,  176. 

Dip,  42. 

Discina,  171. 

Dog,  fossil,  180. 

Dolomite,  244. 

Drift,  79. 

Dromatherium,  179. 

Drowned  lands  and  waters,  101. 


Earth-pillars,  51. 

Earthquakes,  132;  origin  of,  133; 
waves  caused  by,  134;  move- 
ments accompanying,  135. 

Earth's  Interior,  condition  of,  111 ; 
temperature  of,  112;  density 
of,  115. 

Elephant,  fossil,  180. 

Emerald,  251. 

Emery,  223. 

Enstatite,  248. 

Eocene,  155. 

Erratics,  69. 

Eruption,  causes  of  volcanic,  127; 
fissure,  128. 

Evolution,  156. 

Extinction,  162. 

Faults,  47. 

Feldspar,  244. 

Firn,  72. 

Fishes,  fossil,  175. 

Fissure-eruptions,  128. 

Fjords,  103. 

Flagstones,  29,  237. 

Flint,  243. 

Fluorite,  250. 

Foraminifera,  165. 

Formations,  155. 

Fossil  imprints,  38;  footprints,  39; 
raindrops,  39. 

Fossils,  definition  of,  150;  how 
found,  151;  indicating  proces- 
sion in  structure,  152;  charac- 
teristic, 155 ;  kinds  of,  158. 

Franklinite,  218. 

Fringing-reef,  142. 

Faunas,  origin  of,  159;  derivation 
of  types  from  one  another,  159; 
of  the  different  geological  pe- 
riods, 158-164. 

Galena,  212. 
Gaps,  56. 
Garnet,  248. 
Garnierite,  215. 


INDEX. 


265 


Geysers,  yl. 

Glacial  Period,  82. 

Glaciers,  definition  of,  67;  making 

of,  73;  compound,  74;  flow  of, 

75 ;  work  of,  77 ;  retreat  of,  80 ; 

distribution  of,  81. 
Globigerina  ooze,  28. 
Glyptodon,  181. 
Gneiss,  structure  of,  33;  origin  of, 

34. 

Goat,  fossil,  181. 
Gold,  207. 
Gorges,  52. 
Granite,  structure  of,  30;  varieties 

of,  31 ;  origin  of,  32. 
Graphite,  224. 
Grossularite,  249. 
Guano,  240. 
Gypsum,  225. 

Hadrosaurus,  177. 

Heliotrope,  243. 

Hematite,  216. 

Hesperornis,  179. 

Hessonite,  249. 

Hippopotamus,  fossil,  180. 

Hog,  fossil,  180. 

Hornblende,  247. 

Horse,  fossil,  182;  ancestral  forms 

of,  182. 
Horsts,  47. 
Hot-springs,  91. 
Hyena,  fossil,  180. 
Hypersthene,  248. 

Ice- Age,  82 ;  causes  of,  85. 
Ice-caves,  90. 
Ichthyornis,  179. 
Ichthyosaurus,  176. 
Igneous  rocks,  33. 
Iguanodon,  177. 
Iron,  215. 

Jurassic,  155. 
Kaolin,  245. 


Labradorite,  245. 

Laccolite,  129. 

Lake-basins,  60 ;  origin  of,  61 ;  gla, 

cial,  61. 

Land,  making  of,  109. 
Laramie,  155. 
Lava,  122. 
Lead,  212. 
Lepidolite,  247. 
Lias,  155. 

Limestones,  composition  of,  23. 
Limonite,  216. 
Lingula,  171. 
Loams,  239. 
Lydian-stone,  243. 

Magnetite,  218. 

Malachite,  211. 

Mammals,  fossil,  179. 

Mammoth,  183. 

Man,  fossil,  183. 

Manganese,  220. 

Manganite,  220. 

Marble,  composition  of,  23 ;  organic 
nature  of,  25. 

Margarite,  247, 

Marls,  239. 

Mastodon,  183. 

Meadow-lands,  60. 

Megatherium,  181. 

Mercury,  220. 

Mesozoic,  162. 

Mexican  onyx,  243. 

Mica,  246. 

Mica-schist,  35. 

Microlestes,  179. 

Millerite,  215. 

Mineral  waters,  87. 

Miocene,  155. 

Molten  pockets,  114. 

Monkeys,  fossil,  180. 

Monocline,  194. 

Moonstone,  245. 

Moraines,  69,  70;  medial,  74;  ter- 
minal, 84. 

Mountains,  making  of,  44 ;  model- 


266 


THE  EAETH  AND  ITS  8TORT. 


ling  of,  49;  physiognomy  of, 
188 ;  peaks,  190 ;  different  parts 
of,  192 ;  internal  structure,  193 ; 
plateau  mountains,  194. 

Muscovite,  246. 

Mylodon,  181. 

Natural  bridges,  90. 
Natural  gas,  230. 
Natural  selection,  156. 
Nautilus,  172. 
Neve',  72. 

New  red  sandstone,  155. 
Niagara  gorge,  age  of,  86. 
Nickel,  215. 
Notornis,  178. 

Oceanic  basins,  configuration  of, 
94 ;  origin  of,  95 ;  accumulation 
of  sediment  in,  106. 

Oceanic  level,  inconstancy  of,  99. 

Oceanic  recessions,  transgressions, 
99. 

Odontornithes,  179. 

Old  red  sandstone,  155.' 

Oligocene,  155. 

Oligoclase,  245. 

Onyx,  243. 

Opal,  243. 

Orpiment,  214. 

Oriental  amethyst,  252. 

Oriental  topaz,  252. 

Orthis,  171. 

Orthoclase,  245. 

Ox, 'fossil,  181. 

Paleozoic,  155. 

Pearl-spar,  244. 

Peneplain,  53. 

Permian,  155. 

Petroleum,  230. 

Phenacodus,  182. 

Phlogopite,  247. 

Phosphates,  240. 

Pithecanthropus,  184. 

Plain  of  marine  denudation,  104. 


Plateaus,  194. 
Platinum,  222. 
Plesiosaurus,  176. 
Pliocene,  155. 
Pliosaurus,  176. 
Plumbago,  224. 
Porcelain-earth,  245. 
Post-pliocene,  155. 
Primary,  155. 
Proustite,  209. 
Pteraspis,  175. 
Pterodactyls,  177. 
Pudding-stone,  21. 
Pyrargyrite,  209. 
Pyrites,  219. 
Pyrolusite,  220. 
Pyromorphite,  213. 
Pyrope,  249. 
Pyroxene,  247. 
Pyrrhotite,  219. 

Quadrupeds,  fossil,  179. 
Quartz,  242. 

Ravines,  52. 

Realgar,  214. 

Reptiles,  fossil,  176. 

Rhynchonella,  171. 

Ripples,  fossil,  38. 

Rivers,  silting  of,  60. 

Roches  moutonnees,  77. 

Rock-crystal,  242. 

Rock-folding,  41. 

Rocks,   decay  of,   13;   weathering 

of,  16 ;  appearance  of,  36. 
Rock-masses,  physiognomy  of,  202. 
Rock  salt,  225. 
Roofing-slates,  237. 
Rubellite,  250. 
Ruby,  252. 

Sandstones,     formation    of,    20; 

composition  of,  20,  22. 
Sanidine,  245. 
Sapphire,  252. 
Sardonyx,  243. 


INDEX. 


267 


Scaphites,  173. 

Scenery,   development  of,  49,  55; 

of  lake-shores,  64. 
Schist,  35. 
Scoriae,  122. 

Sea,  destruction  by,  105. 
Secondary,  155. 
Sediment  in  rivers,  108. 
Selenite,  226. 
Shales,  29. 
Shearing,  46. 
Sheep,  fossil,  181. 
Siderite,  218. 
Silver,  208. 
Slates,  29,  237. 
Snow,  65. 
Snow-line,  66. 
Soils,  238. 
Sphalerite,  211. 
Spinel,  252. 
Spirifer,  171. 
Stalactites,  90. 
Stalagmites,  90. 
Stibnite,  214. 
Stone-lilies,  168. 
Strata,  signification  of,  39. 
Stratification,  39. 
Striae,  glacial,  69. 
Strike,  45. 

Subsidence,  102,  144. 
Sulphur,  223. 
Sylvaiiite,  208. 
Syncline,  45. 

Terebratula,  171. 


Terraces,  river,  53;  lake,  62;  ma- 
rine, 103. 
Tertiary,  155. 
Tile-stones,  237. 
Time-standard,  154. 
Tin,  212. 

Titanichthys,  175. 
Topaz,  251. 
Tourmaline,  249. 
Trap,  129. 
Trias,  155. 
Triceratops,  177. 
Trilobites,  166. 
Turquoise,  252. 
Turrilites,  173. 

Unconformity,  204. 
Uvarovite,  249. 


Valleysr^ormation  of,  55;  trans- 
verse, 56 ;  physiognomy  of,  196. 

Vanadinite,  214. 

Variation,  160. 

Volcanic-cones,  121;  ash,  122; 
chimney,  126;  neck,  126. 

Volcano,  aspects  of,  117 ;  operations 
of,  118;  characteristics  of,  119; 
dimensions  of,  120 ;  activity  of, 
123 ;  after-history  of,  125 ;  dis- 
tribution of,  130 ;  physiognomy 
of,  188. 

Water,  action  of,  50. 

Zinc,  211. 
Zincite,  212. 


ATTRACTIVE   AND   INSTRUCTIVE 
SCHOOL    READING. 


STEPPING  STONES  TO  LITERATURE.  —  Arnold-Gilbert. 

A  First  Reader  ....    30  cts.  A  Reader  for  Fifth  Grades     .  60  cts. 

A  Second  Reader      .       .       .40  cts.  A  Reader  for  Sixth  Grades    .  60  cts. 

A  Third  Reader        ...    50  cts.  A  Reader  for  Seventh  Grades  60  cts. 

A  Fourth  Reader      ...    60  cts.  A  Reader  for  Higher  Grades  .  60  cts. 

THE  WORLD  AND  ITS  PEOPLE.— Dunton. 

GEOGRAPHICAL  READERS. 

First  Lessons     ....    36  cts.       Modern  Europe  ....  60  cts. 

Glimpses  of  the  World    .       .36  cts.       Life  in  Asia      ....  60  cts. 

Our  Own  Country     .               .    50  cts.       Views  in  Africa        .               .  72  cts. 
Our  American  Neighbors        .    60  cts.       Australia  and  the  Islands  of 

Hawaii  and  Its  People   .       .68  cts.           the  Sea 68  cts. 

NATURE  IN  VERSE  — Lovejoy 60  cts. 

POETRY  OF  THE  SEASONS. —Lovejoy 60  cts. 

BEACON  LIGHTS  OF  PATRIOTISM  -  Carrington 72  cts. 

TWILIGHT  STORIES  —  Foulke .        .        .36  cts. 

BRAIDED  STRAWS.  -Foulke. 40  cts. 

THE  PLANT  BABY  AND  ITS  FRIENDS. —Brown 48  cts. 

THE  ETHICS  OF  SUCCESS.— Thayer. 

BOOK  I.      For  the  Lower  Grades 48  cts. 

BOOK  II.     For  the  Middle  Grades 60  cts. 

BOOK  III.    For  the  Higher  Grades $1.00 

THE  NORHAL  COURSE  IN  READING.  — Todd-Powell. 

Primer 18  cts.  Fifth  Reader      .       .       .  .84  cts. 

New  First  Reader    .       .       .  24  cts.  Alternate  First  Reader    .  .24  cts. 

Second  Reader  ....  36  cts.  Alternate  Second  Reader  .    36  cts. 

Third  Reader     ....  48  cts.  Alternate  Third  Reader  .  .    48  cts. 

Fourth  Reader  ....  60  cts.  Primary  Reading  Charts  .  $10.00 

THE  RATIONAL  METHOD  IN  READING.  — Ward. 

Primer        ......    Complete,  36  cts. ;  Part  L,  22  cts. ;  Part  II.,  24  cts. 

First  Reader     ....    Complete,  36  cts. .-   Part  I.,  22  cts. ;  Part  II.,  24  cts. 

Second  Reader          .       .       .    Complete,  44  cts. ;  Part  I.,  24  cts. ;  Part  II.,  28  cts. 

Third  Reader Complete,  48  cts. 

Manual  of  Instruction  for  Teachers 36  cts. 

Phonetic  Cards         .         First  Set,  36  cts. ;  Second  Set,  48  cts. ;  Third  Set,  36  cts. 


Our  list  comprises  superior  text-books  for  every  grade  of  instruction. 
Our  illustrated  catalogue  and  descriptive  circulars  sent  free  on  application. 

SILVER,  BURDETT  &  COMPANY. 

Boston.  New  York.  Chicago. 


The  Silver  Series  of  Modern 
Language  Text-Books 

Under  the  editorial  direction  of  ADOLPHE  COHN, 
LL.B.,  A.M.,  Professor  of  the  Romance  Languages 
and  Literatures  in  Columbia  University. 

An    Elementary    French    Reader.      By  GASTON   DOUAY,  Assistant 

Professor  of  the  French  Language  and  Literature,  Washington   University, 

St.  Louis.     $1.00. 
France's    Monsieur    Bergeret.       An  abridged  edition  of  France's  series, 

"  L'Histoire  Contemporaine."     Edited  by  F.  H.  DIKE,  Instructor  in  French, 

Massachusetts  Institute  of  Technology.     $1.00. 
Thiers'  La  Campagne  de  Waterloo.     Edited  by  OVANDO  B.  SUPER, 

Professor  of  the  Romance  Languages,  Dickinson  College.     40  cents. 

An  Elementary  German  Reader.     By  FREDERICK  LUTZ,  A.M.,  Pro- 
fessor of  Modern  Languages,  Albion  College.     $1.00. 
Germany  and  the  Germans.     Based  on  the  notes  of  travel  of  P.  D. 

Fischer.     Edited  by  A.   LODEMAN,  Professor  of  German  and  French,  State 

Normal  College,  Ypsilanti,  Michigan.     60  cents. 
Heyse's  Unter  Briidern.       Edited  by  EMIL  KEPPLER,  of  the  Department 

of  Germanic  Languages  and  Literatures  at  Columbia  University.     30  cents. 
Schiller's   Die    Braut  von    Messina.       Edited  by  W.  H.  CARRUTH, 

Ph.D.,   Professor  of  the  German    Language    and  Literature,  University  of 

Kansas.     60  cents. 

An  Elementary   Grammar   of  the   Spanish    Language.      By 

L.  A.  LOISEAUX,  B.S.,  Instructor  in  the   Romance  Languages  and  Litera- 
tures, Columbia  University.     90  cents. 

An  Elementary  Spanish  Reader.  By  L.  A.  LOISEAUX,  B.S. 
90  cents. 

A  Spanish  Anthology.  Edited  by  J.  D.  M.  FORD,  Ph.D.,  Instructor  in 
Romance  Languages,  Harvard  University.  $1.25. 

Zaragiieta.  A  Play  by  MICHAL  RAMOS  CARRION  and  VITAL  AZA.  Edited 
by  GEORGE  C.  ROWLAND,  A.M.,  Assistant  Professor  of  the  Romance  Lan- 
guages and  Literatures,  University  of  Chicago.  With  vocabulary  and  exer- 
cises in  Composition,  based  on  the  Play.  50  cents. 

Manzoni's  I  Promessi  Sposi  (Abridged).  Edited  by  MORITZ  LEVI, 
A.B.,  Assistant  Professor  of  French,  University  of  Michigan.  $1.20. 

Corneille's  Le  Menteur.  Edited  by  J.  B.  SEGALL,  Ph.D.,  Instructor 
in  French  in  the  College  of  the  City  of  New  York.  40  cents. 

OTHER    VOLUMES  IN  PREPARATION. 

SILVER,    BURDETT   &   COHPANY 

New  York  Boston  Chicago 


Other  Publications  of 
Silver,  Burdett  &  Company 

Ballads  of  American  Bravery. 

A  Collection  by  CLINTON  SCOLLARD.     230  pp.,  75  cents. 

A  stirring  and  unexcelled  collection  of  the  bravest  lyrics  which  celebrate  deeds  of  Amer- 
ican courage  and  patriotism.  The  ballads  are  chosen  with  signal  discrimination  and  are 
edited  with  extensive  historical  notes. 

Songs  of  the  Nation. 

Compiled  by  Col.  CHARLES  W.  JOHNSON.      160  pp.,  ?jc, 

A  superb  collection,  embodying  the  patriotic  songs  most  in  demand;  songs  tor  anniver- 
saries and  occasions;  American  folk  songs;  a  group  of  religious  favorites;  rhe  best  college 
songs,  etc. 

Hawaii  and  its  People. 

By  ALEXANDER  S.  TWOMBLY.     3^4  pp.,  75  illustration*,  $1.00. 

A  graphic  description  of  our  new  possession,  timely,  accurate  and  spirited.  The  book 
gives  views  of  the  heroic,  legendary  period,  and  the  authentic  history  since  1778;  it  illus- 
trates present  conditions  and  opportunities. 

American  Writers  of  To-day. 

By  HENRY  C.  VEDDER.     340  pp.,  $1.50. 

Critical  and  sympathetic  analysis  of  nineteen  recent  American  authors  and  their  books, 
interwoven  with  graphic  personal  details. 

The  Old  Northwest. 

The  Beginnings  of  Our  Colonial  System.      By  B.  A.  HINS- 
DALE,  Ph.D.,  LL.D.,  Professor  in  the  University  of  Mich- 

igan. Necw  edition,  revised.  4.20  pp.;  $I>75» 

The  only  adequate  monograph  on  the  development  of  a  section  which  is  Ai  much  a  His- 
toric unit  as  New  England. 

Historic  Pilgrimages  in  New  England. 

By  EDWIN  M.  BACON.      47^pp->  131  illustrations.  $1.50. 

The  narrative  of  early  New  England  and  its  high-souled  founders,  told  picturesquely  to 
readers  who  are  supposed  to  be  standing  on  the  very  spots  where  the  stirring  Colonial  drama 
was  enacted.  Of  keenest  interest  to  all  lovers  of  Yankee-land. 

The  Rescue  of  Cuba. 

An    Episode    in    the    Growth    of  Free    Government.      By 
ANDREW  S.  DRAPER,  LL-D.,  President  of  the  University  of 

Illinois.        192  PP'  Elegantly  and  profusely  illustrated. 


A  judicious  and  inspiring  presentation  of  the  War  with  Spain  as  another  and  importa.it 
step  in  the  world's  movement  towards  human  liberty.  The  best  book  on  the  War,  and  the 
problems  it  has  left  for  our  solution.  "It  reads  like  a  novel,"  says  Lyman  Abbott.  "It  5s 
accurate,"  says  Gen.  Wesley  Merritt. 

These  books  are  sold  by  Booksellers,  »r  will  be  mailed,  postpaid,  on  receipt  of  price. 


35urtiett  anfc  Company 

$et»  got*       Oi3oj3ton       Chicago 


14  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROWED 
EARTH   SCIENCES   LIBRARY 


This  book  is  due  on  the  last  date  stamped  below,  or 

on  the  date  to  which  renewed. 
Renewed  books  are  subject  to  immediate  recall. 


IW  29  T9r3- 

SENTONILL 

AUG  2  3  1994 

U  C  BERKELEY 

T  n  91    Af\m  m  'fi^                                    General  Library 
L(?423o"84s°l")547665                              Univcnity^  California 

